Rumours have been circling the pair for the past few weeks, after petite beauty Mila Kunis has been spotted sporting baggier clothes - and was apparently seen at a pre-natal yoga class.
And now a source, who spoke to E!, says that the 30-year-old Friends with Benefits star is definitely expecting a child with her actor boyfriend.
The pair were seen at the weekend at a Los Angeles Clippers game, where they were caught on the Kiss Cam and delighted fans by leaning in for a smooch.
Ashton, 36, and Mila confirmed their engagement last month, with the Black Swan actress showing off her platinum and diamond engagement ring for everyone to see.
The couple, who are known for their relaxed, down-to-earth styles, originally met on the set of That 70s Show, when Mila was just 14.
Rumours of the co-stars being an item arose as early as April 2012, though they did not confirm they were dating until March 2013.
Kutcher was previously married for six years to 51-year-old actress Demi Moore. The couple split in November 2011 and their divorce was finalised in late 2013.