San Antonio firefighters responded to a small fire in the 500 block of Heimer at the leasing office of the Desert Shadows Apartment Homes.
Firefighters said it was the fourth recent fire at the same location.
"(When) firefighters got here, there was a little bit of flame at the bottom of the door and on the carpet and they put it out. (They) went inside and made sure there was no more fire in there," Battalion Chief Brooke Hildreth said.
Hildreth said it was immediately clear that the fire had been set, due to how the fire was on the outside.
"There was nothing piled up around it," she said. "There was no electricity to that particular area, and there was a pattern."
Hildreth also said it was obvious someone had used an accelerant.
"The damage was actually minimal -- a couple hundred dollars to the door -- but because it's the third time, we're going to look into it a little deeper," Hildreth said.
Arson investigators are taking a closer look and also talking to the apartment manager to find out if there's anyone who would want to target the complex.