The fire with heavy smoke broke out on the fourth floor in NGO Annexe building of the Chennai Divisional Office.
Two fire tenders deployed by the Fire and Rescue services put out the fire after about an hour, Southern Railway officials said.
Nobody was injured in the incident and there was no damage to the building, they said.
An officer Level enquiry has been ordered into the issue, they said, adding a suspected electrical short circuit "cannot be ruled out," as the cause of the fire.