Zendaya, 22, and Jacob, also 22, were snapped in the background of a fan's Instagram photo as they toured the Acropolis of Athens.
The Disney Channel alum dressed down in a white t-shirt, jeans, and glasses as she walked around the tourist attraction with Jacob.
"They looked like they were getting a little cozy. At one point, they were walking with each other and being a little flirty," an eyewitness told Us Weekly.
The actress' friend Darnell Appling and her stylist Law Roach also seemed to be on the pair's trip. Zendaya is set to celebrate her birthday on Sunday, September 1, so it's possible her pals tagged along for the occasion.
Zendaya plays Rue Bennett and Jacob plays Nate Jacobs on the hit HBO drama.
The brunette beauty was recently linked to her Spider-Man costar Tom Holland but they both denied anything romantic was going on between them. Jacob previously dated his Kissing Booth costar Joey King.
Do you think Zendaya & Jacob are dating? Sound off in the comments below!