According to the Russian non-governmental organization (NGO) OVD-Info, Artiom Kamardine, Egor Chtovba and Nikolaï Daïneko have been detained for two months.
The NGO said they were suspects in an investigation opened for “inciting hatred with threats to use violence”.
If convicted, they could face up to six years in prison as Russian authorities crack down on criticism of the ongoing conflict in Ukraine.
On Sunday, the trio took part in a verse reading in front of a statue of poet Vladimir Mayakovsky in central Moscow, where dissident intellectuals gathered during the Soviet era.
The next day, Artyom Karadin was arrested during a house raid.
According to his lawyer Leonid Solov, quoted by the Independent Russian newspaper, Karadin claims he was beaten with a dumbbell and sexually assaulted while in custody.
Channel 112 of the Telegram news service, which is close to Russian police, released a video showing the young man kneeling and apologizing.
During a speech in court tonight, Karadin said the pardon was obtained “under torture”. At the hearing, he appeared with marks and a bandage on his face.
Nikolaï Daïneko was detained during Sunday’s poetry reading and fined for “unauthorized demonstration”. According to OVD-Information, Daïneko was released and re-arrested on Monday.