According to People magazine, Timberlake, 26, is serious about Biel, 25, just four months after his split with actress Cameron Diaz, 34.
Last January, Timberlake and Biel were first spotted together at a Golden Globes party. The two have been spotted together most recently in England, where the SexyBack singer is on tour.
A source told the magazine, "Justin’s in love. He wants to be with her all the time. He’s ready to be serious."
Representatives for Timberlake and Biel have not made a comment on the status of their relationship.