"Happy birthday to Us!!! #leos #305," Rodriguez captioned a photo on Instagram of himself and Lopez at the fete.
The retired New York Yankees star also shared videos on Instagram Stories of himself and Lopez standing next to their six-tier birthday cake, dancing with friends and sharing kisses on the dance floor.
"#305," he captioned one post, referencing the area code for Miami.
"Things are great with them," a source told People in June. "Jennifer still gushes about Alex every chance she gets. The more she gets to know him, the more she likes him. They are definitely very serious."
Lopez shares 9-year-old twins Emme and Max with ex-husband Marc Anthony, while Rodriguez is dad to two daughters, 12-year-old Natasha and 9-year-old Ella, with ex-wife Cynthia Scurtis.
Rodriguez treated Natasha to one of Lopez's concerts in June.