"Aliens exist, there's no two ways about it. There are so many billions of stars out there in the universe that there must be all sorts of different forms of life," metro.co.uk said in the reported citing Sharman as saying to a UK magazine.
She added that although they may not be made up of carbon and nitrogen like humans, "it's possible they're here right now and we simply can't see them".
Helen Sharman is the first British astronaut to go to space.
Sharman, 56, made history when she participated in a mission to the Russian modular space station Mir in May 1991.
In the interview, the astronaut also highlighted how she was often referred to as the first British woman in space, rather than the first Briton.
"It's telling that we would otherwise assume it was a man. When Tim Peake went into space, some people simply forgot about me.
"A man going first would be the norm, so I'm thrilled that I got to upset that order," metro.co.uk quoted her as saying.