Charges against Melbourne teenager Harun Causevic, accused of plotting an Anzac Day terrorist attack, will be dropped today, his lawyer says.

Causevic, 18, has been in custody since April, accused of being part of a plot to drive a car into a police officer, behead them, steal their weapon and launch a public attack at Anzac Day commemorations in Melbourne.

His lawyer, Rob Stary, said Commonwealth authorities would drop the terrorism charges at a court appearance today, though a weapons offence would remain.

Mr Stary said his client had an entitlement to bail over the weapons charges, unless prosecutors could show why he should not be released.

Causevic, from Hampton Park, was the first Victorian to ever be held under a highly secretive preventative detention order (PDO) when he was detained without charge following counter-terrorism raids in April.

Documents released by the Supreme Court in June showed Victoria Police used the PDO to hold Causevic, because of an alleged close association with terrorism suspect Sevdet Besim, and Numan Haider.

Haider was shot dead after attacking police with a knife in 2014.

Besim remains in custody after he was charged with conspiring to commit a terrorist act, and denied bail.

A third teenager, Mehran Azami, was not charged with terrorism-related offences, but remains in custody charged with 19 counts of importing weapons from a Chinese weapons importer.

Causevic was refused bail in May by Melbourne Magistrate Suzie Cameron, after she said he had shown "deep disdain" for police and anti-Australian sentiments.

Following the bail hearing, Causevic's father Vehid Causevic told reporters outside the court that the charge was politically motivated.

"Message from Prime Minister here [is] ... whatever young Muslim who [is] going five times per day in mosque will be charged like terrorists," Mr Causevic said.

Mr Causevic said while his son did not "understand Islam", he had not done anything wrong.

"If you find anybody in this country to say my son has done something, I'll go in jail for all my life," he said.

Police officers in Victoria were no longer allowed to work alone under new safety procedures put in place following the original charges over the alleged terror plot.

The changes meant Victoria Police officers will no longer be allowed to work alone in public places or when dealing with reception duties in low security police stations.

It has also been compulsory for officers to wear bulletproof vests and officers are no longer be allowed to drive or leave marked vehicles at their homes.

"The current environment has seen an increase in threats against police," an email from Victoria Police said in May.

"As a result, Victoria Police is taking steps to enhance the safety and welfare of its employees."