The New York Post reported on Oct. 10 that the two were spotted drinking wine at a New York City hotel last week after the "Mad Men" star hosted the Brooklyn Black Tie Ball.
"They seemed to really be enjoying each other's company," a source told Page Six, adding that the night seemed "low-key."
Jon, 46, and Dakota, 28, hung out for about two hours, the spy said.
The two had dodged dating rumors before. In April, they raised eyebrows when they were seen together at Elton John's 70th birthday party.
Jon hasn't dated anyone seriously since he and Jennifer Westfeldt split in 2015 after 18 years together. He has been linked to Jenny Slate and Kate Beckinsale, but nothing panned out. Dakota split from rocker Matthew Hitt last year after two years of off-and-on dating.
Earlier this year, she spoke to Vogue about her dating life.
"I think I'm a little bit heartbroken all the time, even when I'm in a happy relationship," she said. "I don't do casual very well, and my feelings, even the good ones, get so intense that they hurt."
Jon, meanwhile, recently lamented about single life to InStyle.
"It's hard to be single after being together for a long time," he said. "It's really hard. It sucks."