The 'SexyBack' singer - who has been dating actress Jessica Biel since February - spent the whole evening with the beautiful stranger at a HBO party in New York's Tribeca Grand hotel.
A source told the New York Post newspaper: "Justin was sitting with a bronze-skinned brunette with long brown hair all night at a cocktail table near the dance floor.
"They were obviously into each other. It was just the two of them and he had no entourage at all."
Another source revealed: "He is a notorious flirt. He will f**k anything."
Justin's representative declined to comment on the rumors, saying: "I have no comment on his personal life."
Earlier this month, it was reported Justin and Jessica were planning on moving in together.
The couple are planning to start house-hunting once Justin finishes his world tour next month.
However, Justin, 26, and Jessica, 25, are yet to agree on where they should live.
Jessica wants the 'Shrek the Third' star to move into her Los Angeles home so they can be close to the sea, but Justin is said to be interested in relocating to New York.
Justin supports his restaurant Southern Hospitality with friends in New York.
Filed under: Celebrity • Justin Timberlake •
