"He was really nice, and seemed to be in a good mood," Elias Karroum, manager of the Beruit Cafe, told The Local of his unexpected encounter with Kutcher.
The recently divorced Kutcher, who now stars in the US sitcom "2 1/2 Men", had been to visit Spotify's main offices in posh Stockholm neighbourhood Östermalm earlier on Wednesday afternoon.
Together with a gang from the Swedish company he then visited Karroum's Lebanese restaurant.
"At first no one recognized him, because he snuck in shyly wearing a hat and a big jacket," said Karroum.
"But the restaurant was packed, and rumours soon spread."
Despite recognizing the unexpected star in their midst, fellow guests left Kutcher and his company alone to enjoy their food and drink.
Afterwards, Karroum revealed, Kutcher took the time to pose for a couple of pictures together with guests.
The actor also signed the restaurant's guestbook.
"He thanked us for a nice dinner, and signed his autograph," said Karroum, explaining that the actor's visit was calm, despite having been a surprise.
Around 10pm, Kutcher made his way to the exclusive Lydmar Hotel where Sweden's Princess Madeleine was also dining with friends, according to the Expressen newspaper.
The past year has been a turbulent one for 33-year-old Kutcher, whose recently revealed infidelity scandal led to the end of his six year marriage to Demi Moore.