Jennifer Garner (search) is wearing a rock around the clock.

The sexy "Alias" (search) star was seen happily flaunting what appeared to be a diamond engagement ring on her left hand over the weekend.

As our exclusive photo shows, Garner, 33, showed off the glittering jewel as she filmed her latest movie in Vancouver.

The ring materialized just one week after E! News revealed Garner is at least three months pregnant with Ben Affleck's (search) baby and that he had secretly popped the question.

Affleck's flack refused to comment on the ring and Garner's rep did not return calls last night.

Garner, who's shooting the romantic drama "Catch and Release," (search) first met Affleck, 32, on the set of their action film "Daredevil" (search).

They hooked up following Affleck's abrupt split from fiancee, Jennifer Lopez (search), who went on to wed singer Marc Anthony.

Garner is divorced from actor Scott Foley.