The fire broke out early Wednesday morning at El Guerrero bar near Elm and Adams Ave.
Cal Fire says the blaze appeared to have started on the back wall of the bar.
It spread to the roof, but firefighters were able to put it out quickly.
The fire caused a small amount of damage to the inside of the bar. Smoke from the fire caused the most damage.
Cal Fire says the county will send out a health inspector to determine if the bar is safe to open to serve drinks and food.