Director Marc Forster intends to produce three films in his zombie apocalypse epic.
"Like I said, I like mixing it up," Pitt told the Los Angeles Times from the set of World War Z.
"You need to make it interesting for yourself to make it interesting for other people."
World War Z has been adapted from Max Brooks' novel of the same name.
The movie will star Pitt as a United Nations employee who travels the world in a bid to prevent the spread of a zombie plague.
The cast also features Mireille Enos, Daniella Kertesz, James Badge Dale, Matthew Fox and David Morse.
Forster has described Pitt as "inspiring".
World War Z will open in cinemas on December 21.
> Brad Pitt's 'World War Z' set raided by Hungarian police