Konstantin Lebedev, an aide to opposition Left Front movement leader Sergei Udaltsov, has been formally charged with plotting to organize mass riots and could be jailed for up to 10 years.
On October 18, a Moscow court ordered Lebedev held in custody until at least December 16.
Earlier on the same day, a spokesman for Russia's Investigative Committee, Vladimir Markin, announced the filing of the charge against Lebedev and added that Lebedev had been advised of the charge and denied any guilt.
The move means Lebedev is now closer to being placed under arrest.
Lebedev was taken in for questioning on October 17 along with Udaltsov and another person, Leonid Razvozzhayev, in connection with a film, "Anatomy of a Protest 2," that was aired by the pro-Kremlin television station NTV last week.
The flats of all three were searched on October 17, as was the apartment of Udaltsov's parents.
The film purportedly shows the three involved in a plot to launch large-scale disturbances aimed at toppling President Vladimir Putin.
WATCH: Russian opposition leader Sergei Udaltsov detained.
The film also alleges that Georgian officials helped with the plot, implicating the chairman of the Georgian parliament's Committee for Defense and Security, Givi Targamadze, the Georgian consul to Moldova, Mikhail Iashvili, and three of their aides as having met with Udaltsov in Minsk.
Speaking in Tblisi on October 17, Targamadze denied the allegation.
"First of all, I think it is beneath the dignity of any normal person to comment in detail on Putin's fabricated propaganda, as it is neither the first nor probably the last of its kind," Targamadze said.
"I think, judging from the fact that the whole thing [documentary] did not bring about much public excitement, people perceive it for what it is -- a falsification of Putin's personal pocket television."
Udaltsov was freed from detention later on October 17 and there were no reports that he or Razvozzhayev were being charged.
Markin said the Investigative Committee was looking into information that the group might have been involved in plans for staging terrorist attacks in Russia.
He said if that turned out to be true, Udaltsov and the others, including the Georgian officials, would face terrorism charges.
With reporting by ITAR-TASS, Interfax, AP, and Reuters