Dunst, who was doing publicity for her latest film "Elizabethtown," answered a reporter's question about "Spiderman 3" saying: "We have really great people though as the villains in this film, Thomas Haden Church and Topher Grace -- Venom and Sandman," Zap2it.com reported Monday.
"Maybe I wasn't supposed to say that," she added.
Dunst said she had not gotten a copy of the super-secret "Spidey" script, even though filming is scheduled to start in January.
"But I know the general story," she added. "There's a lot that they're trying to fit into this one."
Sandman is a career criminal whose irradiated body can turn into a sand-like substance and Venom is a symbiotic alien creature that once masqueraded as Spider-Man's costume, Zap2it.com said.