Police were alerted at 1am about the incident at the house, which rents out 12 rooms, on Soi Phaholyothin 52.
When police, a doctor and rescuers from the Ruam Katanyu Foundation arrived at the scene, people in the neighbourhood had already put out the fire.
The charred body of Puttipat Nilbanphot, 31, from Roi Et, was found in front of the bathroom.
Chonmanee Piyawej, 44, the owner of the house, told police that she had been informed by other tenants at midnight that the man had been making noise, disturbing other tenants, so she went to talk to Puttipat but he would not leave his room.
After she left, other tenants heard the man shouting that he had located four “hidden people” or ghosts and threatening to light a fire to chase them away.
The tenants later heard an explosion and the room caught fire, prompting them and neighbours to break in to put out the blaze but the man was already dead, police said.
Neighbours said Puttipat had often been heard talking to himself.