The first and second floors of the nine-story building house an office of the commercial tax department.
No casualties were reported in the incident as employees vacated the building immediately.
District fire officer Borra Ramprakash said the fire was confined to the first floor, and prima facie short circuit seemed to be the cause.
Three fire tenders and forty personnel of the fire department took two and a half hours to extinguish the fire, he said.
Assistant commissioner of commercial tax S V Valli said the fire broke out in the old files section, while the staff worked on the second floor.