"I look exactly like Ryan Reynolds," she told host Jimmy Fallon. "Like, in a shocking way. Sometimes I see a bus going by with a poster on and I think, 'Damn, I look hot. Oh wait, it's not me. I never did that movie, I've been at home.'"
Fallon showed a side-by-side comparison of Beckinsale and Reynolds but remained unconvinced of the pair's resemblance.
"It's weird, right?" Beckinsale asked. "I've wrestled with how -- Obviously, he's not even like, a sort of slightly girly boy bander-type. He's like a big Canadian man. And I really see myself in him."
Beckinsale has never worked with Reynolds and jokingly said she can't be in the same room as the actor.
"One of us would I think explode or something would happen," the star said.
"But I have had boyfriends be in the same room as him when I wasn't there and feel really compromising, or feel like way too intimate," she added. "They sort of know things about his undercarriage that they shouldn't. But they don't."
Beckinsale stars in the new film Farming, which opens in theaters Friday. The movie follows Enitan (Damson Idris), a young Nigerian man fostered by a white family in the U.K. who joins a white skinhead gang.
"The writer/director Adewale [Akinnuoye-Agbage], this is his actual, real story and his real life," Beckinsale said.