  Electron paramagnetic resonance was used to investigate Mn impurity in
Bi$_2$Se$_3$ topological insulator grown by the vertical Bridgman method. Mn in
high-spin S = 5/2, Mn$^2$$^+$ configuration, was detected regardless of the
conductivity type of the host material. This means that Mn$^2$$^+$(d$^5$)
energy level is located within the valence band, and Mn$^1$$^+$(d$^6$) energy
level is outside the energy gap of Bi$_2$Se$_3$. The electron paramagnetic
resonance spectrum of Mn$^2$$^+$ in Bi$_2$Se$_3$ is characterized by the
isotropic g-factor |g| = 1.91 and large axial parameter D = -4.20 GHz x h. This
corresponds to the zero-field splitting of the Kramers doublets equal to 8.4
GHz x h and 16.8 GHz x h, respectively, which is comparable to the Zeeman
splitting for the X-band. Mn in Bi$_2$Se$_3$ acts as an acceptor, effectively
reducing native-high electron concentration, compensating selenium vacancies,
and resulting in p-type conductivity.
