Affleck has stepped behind the scenes in recent years to direct movies including Gone Baby Gone and new drama Argo, and he has picked up a bad habit of miming the lines as his actors are working.
He has now revealed Lively and Renner, who both starred in his 2010 thriller The Town, caught him and ordered him to stop distracting them.
Affleck tells New York Post gossip column Page Six, "(It) is a rather unfortunate tendency... I sometimes will slightly lip-move along with the lines of the actors. The first time I did that was on The Town. During one of Jeremy Renner's close-ups, he was like, 'Can I talk to you for a second? You're mouthing my lines.' It was like, 'OK, I'll stop doing that.' Then Blake said I did it to her... It's a problem, and I'm working on it."
Breaking Bad star Bryan Cranston, who appears in Affleck's latest film Argo, admits he was also distracted by his director's bad habit, adding, "(In a scene) at the end, I could see (Affleck) mouthing my lines. I went, 'You are doing the thing.'... He gets so into (it) that he mouths."