Kunis and Kutcher in baby rumours
The engaged couple will become parents for the first time later this year, according to US reports.
While the pair have yet to comment on the pregnancy rumours, several sites say sources have confirmed that Mila is expecting.
However, reports that the 30-year-old is having twins are said to be false.
An insider told People: "They are both very, very happy. It's still early."
E! News reported that the Jupiter Ascending actress was recently spotted attending a prenatal yoga class in Hollywood.
Hours before the baby rumours broke, Mila and Two And A Half men star Ashton were caught on the Kiss Cam locking lips at a Los Angeles Clippers game in the US.
The pair looked surprised when their images first appeared on the screen but soon got into the spirit of things and smooched, much to the delight of the crowd.
The couple have not officially confirmed their engagement but Mila was sporting an impressive platinum and diamond ring on her engagement ring finger and didn't try to conceal it.
Mila and Ashton, 36, first met when they were co-stars on That '70s Show from 1998 to 2006 and have been dating for nearly two years.