Other Spice Girls stars also sent well wishes to the fashion designer on her special day, as did her children.
Her oldest son Brooklyn, 22, shared a photo of them together and wrote: “Happy birthday mum xx I love you so so much.”
Romeo, 18, wrote: “Happy birthday mum !! I hope you have the most amazing day I love you so much. You’re amazing.”
Her youngest son Cruz, 16, said: “Happy birthday mum have a good day @victoriabeckham.”
Beckham and husband David also share a daughter, Harper, nine.
Bunton shared a collection of photos of the pair together, including with David and Bunton’s partner Jade Jones and from the heyday of the Spice Girls in the late 90s.
She wrote: “Happy Birthday my gorgeous friend and spicy sister @victoriabeckham. Love you to bits
Bandmate Melanie C also sent well wishes, writing: “The happiest of birthdays my darling @victoriabeckham. Sending kisses and love on your special day.”
Geri Horner also shared a message, writing: “Happy Birthday @victoriabeckham!!! Hope you’re having a wonderful day.”
Beckham is celebrating in Miami, where David is part owner of MLS club Inter-Miami.
On Friday she shared pictures from a party with stars including Kim Kardashian and Pharrell, writing: “I feel so blessed to have met so many incredible people here in Miami!
“A big thank you to @pharrell and @davegrutman for hosting last night’s @intermiamicf opening season event.”