The offence, newly introduced after Russia's Feb. 24 invasion of Ukraine, carries a prison sentence of up to five years.
Russia calls its actions in Ukraine a "special military operation" and people risk prosecution if they use the words "war" or "invasion".
Roizman was greeted in the court building by supporters, who shouted "Freedom". He thanked them for coming as he was escorted into court in handcuffs.
Roizman's case centers on a Q&A session held on YouTube, according to the prosecution, which asked the judge to impose a number of restrictions on the former mayor, including on leaving his home and using the internet.
Roizman's former lawyer, speaking outside the court before the hearing, said the case was "politically motivated".
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