A London-based representative for Miller, who became engaged to her "Alfie" co-star last Christmas, refused comment Wednesday on the story, which was posted on People magazine's Web site. The magazine did not name any sources.
Public Eye, the London firm that represents Miller, said it would not comment on her personal life.
The Associated Press sent an e-mail to Tor Belfrage, Law's Los Angeles-based representative, seeking comment early Wednesday.
British media reported this week that Miller, 23, had been seeing Law's friend Daniel Craig (search) while Law was fighting to win her back. Miller and Craig appeared together in the 2004 film "Layer Cake."
Miller was quoted last month as saying, "There's nothing going on between me and Daniel. We were in a movie together two years ago."
Law, 32, earned Oscar nominations for his roles in "The Talented Mr. Ripley" and "Cold Mountain." His screen credits also include "Sky Captain and the World of Tomorrow," "Closer" and "The Aviator."
Craig's credits include the 2005 thriller "The Jacket," starring Adrien Brody and Keira Knightley.
The blond, blue-eyed British-born actor has been mentioned as the new James Bond. Earlier this year, Craig praised the Bond character, calling him "an iconographic figure in moviemaking."
"I think you'd have to be stupid not to consider something like that," he said, but added that he hadn't given the role "any serious thought."