The officers at the Matrosskaya Tishina (Seaman's Silence) pre-trial detention centre were charged with "beating prisoners for non-compliance", Eva Merkacheva wrote on the Telegram messenger app.
She said the officers had not abused prisoners "out of spite", but because they "thought it was okay".
Established by Soviet authorities after World War Two and now run by Russia's Federal Penitentiary Service, the Matrosskaya Tishina facility has over the years held suspected Nazi war criminals, oil tycoon Mikhail Khodorkovsky and several participants of a failed 1991 coup to oust Soviet leader Mikhail Gorbachev.
The newspaper Moskovsky Komsomolets said one of the officers had been charged with four counts of abuse of power, and the other three with one count. It did not say when the crimes occurred.
The men received sentences of up to three and a half years, the report said.
Rights group "Crew Against Torture" - which said it had no knowledge of this case - has documented 3,591 instances of human rights violations in Russia since it began work in 2000 and has secured 167 convictions for abuse perpetrated by government officials.
(Reporting and writing by Lucy Papachristou; Editing by Ros Russell)
