Hawn was quoted in a recent magazine interview as suggesting that the pair, who got engaged last year, had tied the knot.
According to the publication, she said: "When my daughter Kate married an English rock star it didn't worry me. All that matters [is] that the relationship is a good one."
However, Hawn has now denied that the pair are husband and wife on her Twitter page.
Responding to a question from one of her followers, Hawn said: "Darling once again twisted the truth. They aren't married."
Hudson and Bellamy welcomed their first child, a son called Bingham Hawn, last summer.
Watch Matt Bellamy in the Muse video for 'Neutron Star Collision (Love Is Forever)' below: