Alexander Darakov, 29, a customs official, was mumbling as he entered Moscow's Yelokhovo Cathedral Sunday, then stripped during the service, a police spokesman said.
He was taken away by police, then given a psychiatric examination by medics, the police report stated.
While no reason was given for his actions, Dmitry Smirnov, head of the synodal department of the Russian Orthodox Church's Moscow patriarchy, blamed the incident on "spring exacerbation" and a recent disturbance in another church, the Internet news agency Rusnovosti reported.
In February, five masked members of the female punk rock group Pussy Riot entered the altar area of downtown Moscow's Christ the Savior Cathedral and performed a "punk prayer" denouncing the church's ties to government. Three were detained by police and face seven years in prison, the news agency RIA Novosti said Monday.