Sergei Udaltsov, one of Russia's most prominent opposition leaders, has been charged with "plotting mass disorder," RIA Novosti reported.
Udaltsov, the head of the Left Front, faces up to 10 years in jail if he is convicted of conspiring to spread unrest.
He denies the accusations. Shortly before he was charged by the federal Investigative Committee, he told journalists that he would stay in Russia to fight what he claims are politically motivated charges, the BBC said.
"The Putin regime will be on trial," he tweeted.
Udaltsov is the third opposition figure to be named in the case, alongside fellow Left Front members Konstantin Lebedev and Leonid Razvozzhayev.
More from GlobalPost: Leonid Razvozzhayev accuses Russia of torture
According to RIA Novosti, the allegations against them hinge on an investigation by state-run NTV television, which earlier this month aired footage that it claimed showed the trio meeting a Georgian politician in June to discuss plans to overthrow Vladimir Putin.
Udaltsov denies the meeting took place and insists that the footage is fake. His defense lawyers have asked an indepedent expert to examine the video in hope of proving it has been doctored, Russia Today said.
The US has told the Kremlin of its concerns about the treatment of Udaltsov and others involved in the mass protests against Putin's re-election earlier this year, State Department spokeswoman Victoria Nuland said yesterday.
As GlobalPost has reported, Leonid Razvozzhayev claims he was abducted and tortured by Russian security forces, who forced him to sign a confession implicating Udaltsov and Lebedev.
Russia's Foreign Ministry has accused the US of making "unfounded" and "hypocritical" allegations over the case.
Unlike Lebedev and Razvozzhayev, Udaltsov was not taken into custody while he awaits trial, on condition that he remain in Moscow.
More from GlobalPost: Russian opposition forms a shadow government