The Britain's Got Talent judge told the Daily Mail that the stunt was the most embarrassing thing she has ever done for money.
Holden explained: "When I was a student, someone bet me £10 that I wouldn't ride naked round the block on the back of this guy's motorbike. So I stripped off, climbed on and won the tenner.
"I was cuddled up right behind the guy on the bike, so I don't think anyone saw anything. Not until I got off, anyway."
Last month, Holden said that her role on Britain's Got Talent had helped her shed the "minx" tag she earned for cheating on husband Les Dennis with actor Neil Morrissey.