The 45-year-old film star made the claim as she stepped on stage at the People's Choice Awards, after being named Best Movie Actress.
Announcing the nominees, presenter George Lopez had said: 'I have the honour of naming the five white women in America that Tiger Woods has not slept with.'
Winner: Sandra Bullock pulls a face after joking she was Tiger Woods's mistress while accepting her People's Choice Awards
But when Bullock stepped up to collect her award, she said she needed to correct him.
'It's only four women up here who have not slept with Tiger Woods,' she said, pulling an awkward face in front of the audience.
'Just kidding. I'm so just kidding,' she quickly added.
Comedy queen: Sandra laughs with George Lopez onstage
Bullock, whose movie The Proposal was named Best Comedy Film, also made actress Nicole Kidman blush by commenting on their similar hair styles.
'I'd just like to say Nicole and I deliberately did our hair the same today,' she laughed, as cameras cast to the Aussie film star who covered her face in the seats below.
But Bullock's jokes quickly turned to tears when she paid an emotional tribute to her family during the acceptance speech.
'Life is hard sometimes, but we get through with laughter,' she said, choking back tears.
To my Dad - I hope you're feeling better. And my husband, who is my boyfriend, who makes me feel like this every single day.
'He allows me to leave the house and he keeps things settled until I get back so I get to do what I get to do.'
The award came as it was revealed that Bullock has made box office history in the U.S.
Her movie The Blind Side has made her the first leading actress to gross more than $200million in the States - a feat unmatched by stars such as Meryl Streep and Angelina Jolie.
Tall order: Ellen DeGeneres dances with Sandra Bullock as she accepts the favourite comedy movie award for The Proposal
