The incident was reported at 2:20 p.m. and caused system-wide delays of at least 15 minutes until about 4 p.m., BART spokeswoman Luna Salaver said.
Salaver said she did not think the train hit the woman because of her minimal injuries.
Salaver said she did not know why or how the woman was under the train but fire department officials said the woman had been extricated from the tracks.
