The fire was around 9:15pm Friday at Martinez Auto Repair on Lauder Rd. near Trailcrest.
Westfield and Aldine Fire Departments responded and found flames shooting from the back of the building.
They made a fast attack and got the blaze under control before it damaged any of the vehicles inside or outside the shop.
One firefighter electrocuted while battling the flames. He was treated at the scene and released.
Investigators say they believe an electrical box in the back of a garage may have started the fire.