The fire was reported at about 6:45 p.m. by someone who was inside The Original Pepperbelly's Comedy & Variety Theater, located at 849 Texas St.
There were a few employees and customers inside at the time, but police got everyone out quickly.
Fire Chief Vincent Webster says the blaze may have started inside the building. The exterior of the two-story structure, built in the 1960s, remains intact.
The heavy smoke inside the building forced firefighters to call for help from throughout Solano County. Nearly 100 firefighters battled the flames.
The fire was knocked out by about 11 p.m. One crew stayed at the club overnight to make sure there were no flare-ups.
"We have no leads as far as anything being suspicious as far as how the fire started," Battalion Chief Tony Velasquez said. "It's just a normal protocol because it was a five alarm fire."
No injuries were reported and no other buildings were damaged by the fire.
More information about the club can be found at pepperbellys.com/index.cfm.
(Bay City News contributed to this story)