Mumba walked the red carpet at Leicester Square's Odean Theater Monday in the dress, designed by Scott Henshall in tribute to the film, which featured thousands of diamonds woven in a spider web design, Sky News reported Tuesday.
Henshall's design reportedly is the most expensive dress ever made.
Mumba also wore an oversized diamond ring in the shape of a spider, which covered her right hand.
Dunst, 22, wore a white one-shouldered dress by Chanel.
"Spider-Man II" opens throughout Britain Friday.