Navalny, who was detained by police outside his home in Moscow last month, was sentenced to jail for planning an unauthorized demonstration in the Russian capital in January that called for a boycott of what he said would be a rigged presidential election.
Leonid Volkov, a Navalny ally, wrote on Twitter on Monday morning that Navalny had been taken to a police station as he walked out of jail and was again being accused of violating protest laws.
Navalny, 42, has said his jail sentence was designed by the authorities to prevent him from leading protests against unpopular pension reform across the country earlier this month.
More than 800 people were detained nationwide during those demonstrations.
(Reporting by Gabrielle Tétrault-Farber; Editing by Paul Tait)