"They are both very, very happy," a friend of the couple told People. "It's still early."
The exciting news comes one month after the couple's engagement was revealed. The long-time friends, and former That 70s Show co-stars, started dating in 2012.
Mila, 30, and Ashton, 36, were spotted kissing at a basketball game in LA on Saturday, where the bride-to-be happily showed off her beautiful engagement ring.
The down-to-earth stars locked lips when they were spotted by the Kiss Cam, much to the delight of the crowd. "It was so cute," a source told E! News.
It remains to be seen whether Mila's pregnancy means wedding plans are put on hold for the time being. According to reports, the couple were in no hurry to walk down the aisle, with friends reporting that they haven't started planning their big day yet.
Ashton and Mila have known each other since meeting on the set of That 70s Show in 1998. "He was so love with (Mila) for a while when they worked together," a friend of the actor told People in 2012, when it was first reported the couple were dating.
"He thought she was a goddess, was always talking about how beautiful she is."