The Hollywood actress, who has been engaged to Justin since 2012, opted for a low-key dinner at the trendy Soho House in Los Angeles.
Jennifer and Courteney were spotted dining with Tobey Maguire's wife Jennifer Meyer and Jennifer's hairstylist Chris McMillan, according to E! News.
The best friends have been through thick and thin together, with Courteney supporting Jennifer through her painful divorce from Brad Pitt, and vice versa when Courteney ended her 14-year marriage to David Arquette in May last year.
"There's absolutely no judgement in Court," Jennifer has recently said. "You'll never feel scolded. She's extremely fair, ridiculously loyal and fiercely loving.
"I've slept in her guest bedroom a lot. Without giving away too much of my private stuff, all I can say is she's been there for me through thick and thin."
While rumours have suggested that Jennifer and Justin's relationship is on the rocks, the Iron Man 2 actor couldn't celebrate with his beloved birthday girl as he was on the opposite side of the country.
Justin, 42, is currently working on new HBO show The Leftovers in New York and was seen filming on set during the day of Jennifer's birthday. Later that night the director and screenwriter attended the Deth Killers of Bushwick store launch party in downtown Manhattan with Orlando Bloom.
Meanwhile, a huge bunch of balloons in all different shapes and colours was seen being delivered to the Bel Air estate that Jennifer and Justin share, and were possibly a gift from her future husband.