Crews were dispatched to the school, located at 2201 Encinal Ave., shortly before 3:30 a.m. in response to a fire alarm.
They arrived to find two small fires burning in a classroom, and were able to douse the flames using fire extinguishers, fire officials said.
The damage to the building was "pretty much cosmetic," Alameda fire Division Chief Douglas Long said.
A message on the high school's website noted that school is in session as usual Wednesday. "Campus is safe and all classes will resume as scheduled," the message states.
The fire remains under investigation by the police and fire departments.