Earlier this month, the Moscow prosecutor's office had asked the court to declare FBK as an extremist group and its staff as extremists.
Imprisoned Kremlin critic Alexei Navalny said he felt "pride and hope" after learning about the mass protests held across Russia on Wednesday.
Navalny likened his detention conditions to "Orwell's 1984" in an Instagram post on Monday.
Russia's media watchdog accuses the social network of failing to remove content related to drug use, suicide and child pornography. Twitter is also used widely by supporters of Kremlin critic Alexei Navalny.
Police on Sunday detained protestors outside the Matrosskaya Tishina prison in Moscow, where jailed opposition leader Alexei Navalny is supposedly being held.
Thousands turned up to support Russia's jailed opposition figure. Police detained hundreds and were filmed hitting protesters.