Scarlett Johansson may top many of Hollywood's sexiest women lists, but she says she would turn down Playboy mogul Hugh Hefner's offer to bare all for the lads mag.

"No, I'm a private person," the actress told Extra. "I'd like to keep everything under wraps, within reason."

Scarlett, 24, also said she isn't concerned that she tied the knot with husband, Canadian actor Ryan Reynolds, at such a young age - the pair wed in September.

"I can't worry about it anymore," she laughed. "Too late!"

Scarlett was promoting her upcoming sci-fi thriller movie The Spirit, in which she stars alongside Eva Mendes and Samuel L Jackson. It comes out in the US on Christmas Day.