The two were spotted exiting the same flight in Los Angeles after attending a tech conference for their joint venture, We Are Thorn.
The former couple, who split in 2011, were seen talking as they walked out of the terminal together. A source confirms to E! News that "Demi did not want to be photographed together, but Ashton convinced her to walk with him."
Demi walked into the parking structure of the airport with a female friend, while Ashton shouted, "Bye, Demi!" from the sidewalk.
The actress was wearing a brown sweater over a beige dress and leggings for her flight. She also carried a large tote bag and was sporting reading glasses at the terminal.
Ashton also looked comfortable for his flight in a cardigan sweater and baseball cap.
The organization, which was previously dubbed the Demi and Ashton Foundation, was created in 2009 and aims to use technology to "effect positive changes in the world."
According to Thorn's site, the company's main focus is to "disrupt and deflate the predatory behavior of those who abuse and traffic children, solicit sex with children, or create and share child pornography."
Ashton tweeted Monday night about the event, saying, "Thank you to everyone on the @thorn tech task force. Your dedication and pursuit of a better world will echo for generations."
Meanwhile, Ashton's girlfriend Mila Kunis was in Toronto promoting her latest flicks Blood Ties and The Third Person, alongside Olivia Wilde.
Mila heated up the red carpet Monday evening in a low-cut white Burberry dress. She accessorized the sexy look with a pair of stunning emerald drop earrings and classic snakeskin pumps.
The 30-year-old brunette has been at the center of engagement rumors recently, after she was spotted in Los Angeles wearing a band on her wedding finger.
No official word yet from her rep as to whether or not the ring was a gift from beau Ashton.
The Two and a Half Men star filed for divorce from his wife of six years in December 2012, almost a year after they announced their separation. Demi filed a response three months later seeking spousal support.
The case is still being processed in Los Angeles Superior Court and has yet to be finalized.