Roizman, who served as mayor of Yekaterinburg, was detained in a move seen as part of the Kremlin's efforts to silence the remaining opposition in the country.
Russian opposition politician Yevgeny Roizman, the popular former mayor Yekaterinburg, was arrested on Thursday over a social media post from 2021 which he denies authoring, his attorney said.
The head of a charitable foundation, and one of the last remaining Russian opposition figures not to be detained or to have fled the country, Roizman, 60, "was taken to the police station," Vladislav Idamjapov told the state-run TASS and Ria Novosti news agencies.
The authorities are expected to decide whether or not he will be placed in administrative detention.
According to local outlets, Roizman was arrested on suspicions of having shared a publication of Alexei Navalny's Anti-Corruption Foundation on VKontakte, Russia's version of Facebook, in May 2022.
Navalny's foundation has been designated an "extremist" organization by the authorities, who dissolved it in 2021.
His lawyer rejected the accusation, saying that Roizman never had a personal account on VK and had no connections to the group the document was shared with.
A weakened Russian opposition is now crushed
Roizman was previously arrested in August, before being released on parole, pending trial after being accused of "discrediting the army" by criticising Moscow's full-scale invasion of Ukraine.
Prior to that, he had already been fined three times for his vocal criticism of the aggression against Ukraine.
Decimated by previous waves of repression, the Russian opposition has been rendered non-existent since February 2022.
The few remaining notable critics of President Vladimir Putin are believed to have emigrated or already imprisoned.
Recently, the leader of the Solidarnost opposition movement Ilya Yashin was sentenced to eight and a half years in prison for condemning the war. Another key opposition figure, Vladimir Kara-Murza, is being tried on similar charges.