The singer made the claim while presenting Gary Barlow with the 'Classic Songwriter' gong at yesterday's Q Awards in London, reports The Sun.
Before presenting the accolade, Martin quipped that his favourite bands were "U2 and five handsome, strapping men from Stoke and Manchester".
He added: "I'm not afraid to admit it, they made me ask the question 'Am I gay?'"
However, later in the awards ceremony, U2's Larry Mullen cheekily shot back: "Chris Martin, I have the answer for you - you are gay," while collecting the 'Greatest Act Of The Last 25 Years' award.
Meanwhile, Coldplay walked away with the 'Best Band In The World' prize at the show on the same day their fifth studio album Mylo Xyloto went on sale.
Speaking about working with Rihanna on the record, Martin joked: "Rihanna was pretty ugly and grumpy but we got past that."
He concluded: "She's the best singer in the world and we thought what our album needed was the best singer in the world.
"We asked her very nervously and she said yes, which we were very grateful for."
> Adele scoops double at Q Awards 2011
Watch the music video for Coldplay's new single 'Paradise' below: