Nick Cannon has laughed off rumours that Mariah Carey cheated on him with rapper Nas.

The America's Got Talent host denied the adultery allegations, saying that it's "amazing" that the couple will soon celebrate their sixth wedding anniversary.

"It's amazing to me when I hear that stuff. Nas is probably one of the best rappers to ever do it," he told US shock jock Howard Stern on his radio show.

"He's a friend of mine, he's a friend of hers. She went to his birthday party and I think I was in LA... We actually talked about this before. It'd be very difficult to make me jealous. I'm probably one of those dudes that's really secure in my relationship."

Nick, who has two children with Mariah, surprised his wife with some "butterfly bling" on her birthday on March 27.

"Nick surprised me for 3/27 with a stellar diamond bracelet encrusted with 3 floating butterflies!" the singer tweeted with a close-up photo of her new jewellery.