The fire broke out in a grass field adjacent to the so-called Red Guard community radio station in tambon Khukhod and spread rapidly over vast areas because of windy conditions.
A few loud explosions were heard but authorities said they were caused by discarded used spray canisters left in the field.
Post Today quoted Pol Col Soonthorn Himarat, investigation chief of Pathum Thani police station, as saying that the fire was caused by sparks from a metal-cutting tool used by a soldier who was disassembling communication devices on the premises.
Soldiers did not allow reporters to get close to the scene.
Three fire trucks were sent in to battle the fire. Firefighters took about two hours to completely put out the blaze.
The 10.565 MHz radio station run by Ko Tee, whose real name is Wutthipong Kochthammakhun, was ordered shut early this week after it defied an order by the National Council for Peace and Order requiring all unauthorised community radio stations to stop broadcasting.