Witnesses say it happened on the 38-Geary line at around 8:40 a.m. at Geary Boulevard near Jordan Avenue.
The principal of nearby Roosevelt Middle School says one of his students was involved.
The boy was between 11 and 13 years old. He went to the hospital but there is no word yet on his condition.
Muni says the doors are not supposed to open while the bus is moving.
