San Diego police Det. Gary Hassen said the bus rear-ended a minivan at a stop sign, then veered into the house Wednesday in the Emerald Hills neighborhood.
Hassen says the female bus driver may have had a seizure and lost control of the vehicle.
The bus driver, plus a 44-year-old woman and her 9-year-old son in the van were taken to hospitals for treatment of minor injuries.
The house sustained extensive damage. Nobody was home at the time.