Alexei Navalny said a court ruling held inside a police station was a mockery and called for street protests.
Dozens of his supporters gathered outside the Moscow police station where he was being held and shouted “disgrace” and “Putin resign”.
Mr Navalny was held soon after his flight from Germany arrived on Sunday.
Russian prosecutors say he violated the parole terms of a suspended sentence for embezzlement. He says the charges are politically motivated.
Last August, Mr Navalny, 44, was almost killed in a nerve agent attack, which he blamed personally on Russian President Vladimir Putin.
The Kremlin denies involvement. The opposition politician’s allegations have, however, been backed up by reports from investigative journalists.
On Sunday, big crowds gathered at Moscow’s Vnukovo airport to greet Mr Navalny’s flight from Berlin – but in a last-minute decision the authorities re-routed the plane to another airport in the capital.
A makeshift courtroom was organised on Monday at a police station in Khimki, on the outskirts of Moscow, where Mr Navalny had spent the night.
