Three members of the group were arrested for staging an anti-Vladimir Putin demonstration in a church in February.
Court press secretary Ksenia Lyapina told ITAR-Tass a man with an ax attempted to attack Judge Yelena Ivanova in the courthouse where she was overseeing the performance artists' trial.
The judge pressed an alarm button, summoning help, and the man was taken into custody, the news agency said.
The man's identity and what charges he might face were not reported.
Swim Week Miami Beach 2014 [PHOTOS]