No casualties have been reported as the incident took place after the office hours, they said.
Four fire tenders were rushed to the spot to bring the situation under control. The fire broke out at the first floor of the building and it took almost half-an-hour to douse the flames, a fire brigade official said.
"We detected the source of the fire and managed to douse the flames on time," the officer said, adding that the cause of fire is not known yet.
The building is located near Raj Bhavan.