Moore filed for divorce from Kutcher after six years of marriage in November, citing the violation of "sacred values" as the cause of the couple's split. Kutcher had been rumoured to have had an affair in the months before the divorce filing.
An eyewitness told Us Magazine that both stars happened to be dining at a private member's club in Hollywood on December 1 when Moore and a male companion spotted Kutcher.
"She approached his table. He gave her a hug, and they spoke for a few minutes," the insider added.
Kutcher and Moore apparently remained "polite" during the conversation, but the source described the run-in as "very awkward".
Reps for the two stars have not commented on the alleged meeting.
A friend of Moore said last week that the actress has already "moved on" from Kutcher and is looking to start dating once again.
Moore and Kutcher married in September 2005 after dating for more than two years. They have no children together.
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