Rebekah Armstrong told The Sun she was woken by a noise coming from the garden.
When she realised husband Ian was not in bed she went downstairs to see what was happening.
Rebekah said: "Ian was mowing the lawn completely starkers. I dread to think how long he'd been there but he'd nearly finished.
"I was going to wake him but I have always been told it can be dangerous to disturb someone who is sleepwalking.
"In the end I just unplugged the mower, went back to bed and let him get on with it."
Ian, 34, later got back into bed and didn't believe Rebekah when she told him what he'd been up to.
Rebekah added: "It wasn't until I told him to look at the soles of his feet that he finally believed me - they were filthy." - Ananova