Los Angeles police Sgt. Mark Ro says uniformed vice officers were conducting a routine investigation of the theater shortly before 9 p.m. Wednesday and saw Willard engaging in a lewd act.
He says Willard appeared to be alone.
The 72-year-old actor was booked at the Hollywood police station on suspicion of committing a lewd act in public. Ro says Willard was released after midnight without posting bail.
A call to Willard's agent, Mike Eisenstadt, seeking comment wasn't immediately returned Thursday morning.
Willard was nominated four times for Emmys for guest roles on TV's "Modern Family" and "Everybody Loves Raymond." He also has appeared in other Christopher Guest mockumentary films, including "This is Spinal Tap" and "Waiting for Guffman."