The quake hit at 6:01 p.m. PT, the agency says, 182 kilometres southwest of Port Hardy, B.C.
CBC meteorologist and seismologist Johanna Wagstaffe said the quake was felt by residents in the towns of Ucluelet and Tofino, on the island's west coast.
"We have had a report of some shaking, about 30 seconds long," Wagstaffe said. "And a report in Winter Harbour on the northern tip of Vancouver Island of some swaying for about 15 seconds."
The tremor was felt at least as far away as Cowichan Bay, on the island's east coast, north of Victoria, where Catherine Hamilton said she got a bit of a shake.
"The canisters in my kitchen were rattling together. Then it stopped and repeated itself. My husband did not believe me," Hamilton said in an email to CBC News.
There is no word yet on injuries or damage. A tsunami alert was not issued.
A much more powerful 7.7 quake struck off the coast of Haida Gwaii on Oct. 27, a few hundred kilometres north of Wednesday evening's tremor.
That earthquake caused some local minor damage in the Haida Gwaii island chain off the north coast of B.C., but no injuries.