Awkward moment for Keke Palmer at SXSW … she was doing a panel for her new movie when a man in the crowd approached the stage and asked her to marry him … and it’s all on video.

TMZ obtained footage of the super awkward proposal … the guy is sitting in the front row and then he walks to the edge of the stage, drops to one knee and proposes.

Keke looks shocked and stunned … ditto for the rest of her “I Love Boosters” costars who were also on stage … including Demi Moore, Naomi Ackie and Eiza Gonzalez.

The actress plays it cool and calmly tells the man she can’t marry him … because she doesn’t know him. Overall, Keke’s pretty nice about denying him.