De Armas shared photos with Affleck, 47, Thursday while celebrating her 32nd birthday with The Way Back actor.
In a slideshow, de Armas posted pictures that showed her and Affleck enjoying a meal and cake in a desert location and Affleck embracing her around the waist.
"Thank you all so much for the birthday wishes and love! Cheers to another great year," she captioned the post.
De Armas also shared a video of herself hitting a star-shaped piñata. Affleck can be heard cheering her on in the background.
"I love it!" the actor says. "Más! Más!"
Actor Garret Dillahunt and actresses Priyanka Chopra and Jurnee Smollett were among those to wish de Armas a happy birthday in the comments.
"Aaaahhhh Happy birthday hermana!" Dillahunt wrote.
"Happy birthday love," Chopra said.
Affleck and de Armas were first linked in March after they were spotted in de Armas' hometown of Havana, Cuba. The couple met on the set of the upcoming film Deep Water.
Entertainment Tonight reported this month that Affleck and de Armas have been self-isolating together amid the coronavirus pandemic.
"Ben is in a great place and is very happy with Ana. They are low-key," a source said. "He and Ana are getting to know each other during this quarantine time and are excited to see where it goes."
Affleck was previously married to Jennifer Garner and has three children, Violet, 14, Seraphina, 11, and Samuel, 8, with the actress. He said on ABC News in February that he was single but open to a "meaningful" relationship.
De Armas is known for starring in the 2019 film Knives Out and will appear in the new James Bond movie, No Time to Die. She and Affleck play a married couple in Deep Water, which opens in theaters in November.