Jessica Biel -- ROCKIN' OUT at Justin Timberlake Concert

Wanna see Jessica Biel get straight up funky during the Justin Timberlake concert last night?? Then you've come to the right place!

Jessica couldn't help herself while watching her husband perform SexyBack during a post-awards show concert in London Wednesday night ... shaking her ass, bouncing around to the beat and waving her hands around ... a lot.

One person in our office, who is FAAAARR from a dance expert, described the footage as, "Jessica Biel dancing like a nerd."

Whatever ... she still got to go home and bang Justin Timberlake.