The U.S. Geological Survey reported that the earthquake struck at 2:29 p.m. and had a depth of 4.2 miles.
The quake was centered about 3 miles north-northwest of Daly City and 9 miles southwest of San Francisco City Hall, according to the USGS.
The BART procedure for earthquakes is for trains to stop at the next station following a quake, spokesman Linton Johnson said.
The trains wait five minutes at that station "to see if it was the big one or a precursor to the big one," and then resume moving at half-speed while crews go out to inspect the tracks, Johnson said.
The procedure usually causes residual delays of about 10 minutes for about a half-hour following a minor quake like the one this afternoon, he said.
Muni service was also briefly disrupted due to the quake. Muni spokesman Paul Rose said trains and cable cars were moving slowly after the temblor, but were back in regular service as of 3:20 p.m.
Bus service was not affected, Rose said.