Keira Knightley leaving a London theatre after her performance, Feb. 2, 2010. (WENN.COM)

A man has been arrested for allegedly harassing Keira Knightley outside the London theatre where she is starring in a play.

The actress is said to have alerted police after feeling threatened by a fan who regularly waited outside a stage door at the Comedy Theatre, where she is performing in The Misanthrope.

A 41-year-old man was apprehended outside the venue and taken into custody on Thursday, before facing questioning on Friday, according to Britain's The Sun.

A source tells the newspaper, "Keira felt threatened by this guy who turned up a number of times and tried to speak to her. He did not make any specific threats to her but she was concerned enough to call the police."

A spokesperson for the Metropolitan Police confirms, "A 41-year-old man was arrested on suspicion of harassment on Thursday. The arrest follows concern expressed by a woman."