The Anna Karenina star said that she finds it easier to reveal her body than her personal life.
Knightley told The Mirror: "I'm not prudish when it comes to nudity. If the role calls for nudity, then I'm going to be naked. I'm not afraid to expose myself that way."
In the new film adaptation of Leo Tolstoy's classic, the British actress appears in several love scenes where she has to reveal her body. She has also stripped in earlier movies including 2008's Edge of Love.
Knightley confessed that she finds conveying personal relationships on screen much more challenging.
"I'm much more worried about revealing personal sides to myself, which I find harder to do," she said.
"The hardest thing to capture about love is the actual physical intimacy between two people.
"The way two people behave when they are next to each other and touching each other, holding hands, resting your head on your partner's shoulder.
"In your personal life, you generally don't think about the fact you're touching your partner. That's a difficult things to capture on film."