The Houston Fire Department responded to the scene at 1 p.m. at the corner of N. MacGregor Way at Calhoun.
Firefighters arrived to find smoke and fire showing from the second story of the 40-unit apartment complex.
One resident suffered burns to their hands, and 20 others had to be evacuated from the building.
HFD is investigating what started the fire.
"It's too early to determine a cause, but we know that it probably started on the second floor, we have arson investigators on the way to determine a cause more precisely," said HFD spokesperson Martee Boose.