Htay Kywe has been in hiding since the crackdown
Among those detained was Htay Kywe, who led some of the first marches and was a prominent activist in a 1988 uprising.
The arrests came as thousands attended a pro-government rally in Rangoon, many of them apparently under duress.
UN envoy Ibrahim Gambari, who met junta leaders earlier this month, is preparing for another visit to Burma.
The arrests are going on, despite assurances given by the authorities to the UN
Daniel Alberman, Amnesty International
Other leaders detained overnight included Thin Thin Aye, also known as Mie Mie, and Aung Htoo, according to human rights group Amnesty International.
Hiding
Amnesty fears the detainees are at risk of torture and ill treatment.
"All three were involved in the early demonstrations at the end of August of this year and then basically went into hiding and were sought by the authorities, and they were only discovered today," Amnesty representative Daniel Alberman told the BBC's Newshour programme.
Burmese activists and dissidents say several thousand people have been taken into detention since troops and armed police cracked down on the protests at the end of September.
The Burmese military says it is also holding more than 100 monks arrested in recent weeks, though correspondents say the true figure is much higher.
Mr Alberman said UN pressure had not prevented the arrests.
Rangoon was the focus of recent anti-junta protests
"There are still individuals free and hiding from arrest - we know of that - but the number is dwindling."
The government says 10 people were killed in the crackdown, though opposition groups say the toll was many times higher.
Rally
On Saturday, the junta organised the first pro-government rally in Rangoon since the suppression of the protests.
Officials said 120,000 people had attended the event, though there is no way to independently verify the figure. Burmese dissident groups said the number was much smaller.
There are reports of people being bused to the rallies and being paid cash to attend, while one participant told AFP news agency that every factory in the city's industrial zone had been obliged to send 50 participants to the rally.
The crowd chanted slogans denouncing Western countries and the foreign media, including the BBC, which Burma's military rulers accuse of fomenting the recent protests.
Other slogans denounced "internal and external destructive elements" - a reference to detained opposition leader Aung San Suu Kyi and Western countries.
Mr Gambari is due to arrive in Thailand on Sunday, hoping to prepare the ground for a follow-up visit to Burma.
"I have instructed him to first visit the region to discuss with the leaders to create the necessary political atmosphere so that he'll be able to visit Myanmar sooner than mid-November," UN Secretary General Ban Ki-moon told reporters in Washington on Friday.
Earlier this month, Mr Gambari travelled to Burma and met the ruling junta and Ms Suu Kyi.
Earlier this week, the UN Security Council issued a statement condemning the violent suppression of anti-government protests.
The Burmese junta said in response that it "deeply regretted" the statement.
China had previously used its veto to block criticism of Burma's rulers, but said the council statement was meant to support mediation efforts by Mr Gambari.
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Tres de los últimos líderes del Grupo de Estudiantes de la generación del 88, que ha dirigido recientes manifestaciones prodemocracia en Myanmar (ex-Birmania), han sido arrestados por la Junta Militar que gobierna el país.

La ola de protestas, que comenzó el 15 de agosto de 2007, fue causada por la decisión de la junta de remover subsidios a los combustibles, causando que los precios del diesel y el petróleo incrementaran drásticamente.

Las medidas que ha tomado la Junta Militar para con las protestas –en la cual se estima podrían haber sido asesinadas 200, aunque la Junta reconoce poco más de una docena– ha sido condenada universalmente, incluyendo a Estados Unidos, Reino Unido, Francia y Argentina entre otras naciones. El 12 de octubre, el Consejo de Seguridad de Naciones Unidas declaró que "deplora fuertemente" la respuesta de Birmania para con las protestas.

Los tres líderes –llamados Htay Kywe, Mie Mie, y Aung Thu– fueron arrestados el sábado por la mañana en Rangún, de acuerdo a fuentes. Amnesty International, un grupo que vela por los derechos humanos, expresó gran preocupación por la seguridad de los tres activistas, declarando que se ven amenazados de sufrir tortura y mal trato.

El sábado, miles acudieron a una marcha pro-Junta en Rangún, en la cual los participantes repudiaron a los países y la prensa occidentales. Los participantes habrían sido pagados para atender a la manifestación y fueron transportados por autobús.

Un participante declaró a la ''Agence France-Presse'' que cada fábrica de la zona industrial fue obligada a enviar un mínimo de 50 participantes.