The BAFTA-winning actress confessed that she feels particularly uncomfortable during close camera shots.
She told Metro: "The closer a camera gets to me, the worse I am at acting, it completely throws me."
Mulligan revealed that she prefers stage acting, saying: "The best moment of my career to date was doing The Seagull on Broadway.
"It was a couple of years ago, before all that stuff happened with An Education.
"Nothing's topped it, the feeling of being on that stage. It's so immediate and so consuming in a way that film isn't."
The 26-year-old added: "Film's so stop and start and that often makes me act badly. But on stage I'm blinded by the lights."
However, the star praised Shame director Steve McQueen for being an "actor's director".
"There's a whole scene with me and Michael, and we're sitting on the sofa and the camera doesn't move once, so you don't feel the camera. Steve feels very much like an actor's director," she said.
> Carey Mulligan: 'Playing an exhibitionist in Shame was a relief'
> Carey Mulligan: 'An Education role changed my career'
Watch Carey Mulligan talking to Digital Spy about Shame below: