The 6.2-magnitude tremor was recorded at 7:29 p.m. PT Monday at a depth of about 10 kilometres and was centred about 260 kilometres southwest of Prince Rupert, the U.S. Geological Survey said.
There were no reports of injury or damage.
It is very close to the same area of Saturday's 7.7 magnitude quake.
The U.S. National Weather Service said the latest quake was not expected to generate a tsunami.
The tremor came as questions are being raised about the B.C. government's response to the weekend earthquake off the northwest coast, after officials took more than half an hour to issue a tsunami warning.
Seismologists say aftershocks like the latest one are normal. But Masset fire chief Stephen Grosse said that comes as little comfort to residents.
"People are like pins and needles around here right now," Grosse said. "People are too nervous. It scared them pretty bad. They still don't know who to trust, or if they should trust anybody."
Grosse said the rush to stock up on gas, water and non-perishibles left one gas station empty over the weekend.