Baker firefighters received a call about 10:18 a.m. on Feb. 6 and arrived to find smoke pouring out of the first floor window of the two-story building at 4807 Groom Rd., said Howard Ward, Baker FD's Public Information Officer.
The structure, formally the Baker Branch of the East Baton Rouge Parish Library, is now the home of the Baker Masonic Lodge 441.
Ward said nobody was in the building at the time of the incident.
Forced entry through a door was made by firefighters, Ward said, and the fire was quickly extinguished.
Investigators initially thought the fire started in a back room of the building on or near a small table which may have had a coffee pot left unattended. Officials now say the cause is not what they initially assumed, and they are continuing the investigation.
Arson investigators with the Baton Rouge Fire Department are assisting in the investigation.
Zachary Fire/Rescue and Baker Police also responded to the scene.
Ward said the fire was under control by about 10:32 a.m.
Monetary damages to the interior of the building are unknown at this time, but more details will be forthcoming as the investigation continues, said Ward.