Oprahquietly performed a super-kind gesture ... calling Ahmaud Arbery's mother to pay her respects on what would have been his 26th birthday.
Ahmaud's mom, Wanda Cooper-Jones, tells TMZ ... Oprah personally reached out Friday, offering condolences over her son's murder and wishing Ahmaud a happy birthday.
Wanda says she was in disbelief when she answered the phone to find Oprah on the other end. She's still not sure how O got her number -- O's got her ways -- but Oprah said she was thinking of Ahmaud's family on what should have been his special day.
Oprah also told Wanda she hopes the family gets justice, but stopped short of saying what she thinks justice would be. Wanda also says O was happy Ahmaud's murder suspects, Gregory McMichael and Travis McMichael, were finally arrested.
Oprah's not stopping with a cordial call ... Ahmaud's mom says she's sending something in the mail, but the contents remain a mystery.
O and her family also walked 2.26 miles Friday to honor Ahmaud on the day he would have turned 26.
As we reported ... lots of celebs showed their support for Ahmaud by walking 2.23 miles, which represents the date Arbery was shot and killed while jogging in Georgia on Feb. 23.
Ahmaud's mom tells us other celebs have reached out in an outpouring of support in the wake of her son's murder, which she calls "a senseless act."
Wanda says Gayle King called and offered kind words Thursday, and Rev. Jesse Jackson called and told her he wants to visit her and Ahmaud's family when it's safe to travel again.