The blaze started just before 8 p.m. at the Park Haven Apartments in the 4200 block of Camino De La Plaza, across the street from Willow Elementary School.
No one was home at the time and no injuries were reported.
Suspicious materials were outside the first-floor three-bedroom unit, including a torch on the ground about 20 feet from the back windows. Similar materials were found inside. The Metro Arson Strike Team was investigating the fire as suspicious.
It has not been determined whether those materials were used to start the fire.
Neighbors used extinguishers and helped prevent the blaze from spreading to other units.
The estimated loss to the unit and to the residents' belongings was about $50,000