recent study conducted at University of Illinois at Urbana-Champaign suggests just that. Gunwoo Yoon, lead author on the project, told Reuters Health, "The biggest finding of the paper is that virtual representation of your avatar can profoundly affect real world behavior [...] And the fascinating thing is that the participants did not perceive these effects."
The experiment involved a group of college students that played for five minutes as one of three avatars in a game: Superman (hero), Voldemort (villain), or a circle (neutral). After the gaming session, participants then had to decide how much chocolate sauce or chili sauce to give to other participants in a supposedly unrelated taste test. As it turns out, those who used the Superman avatar poured twice as much chocolate sauce (symbolizing a "good" deed) than chili sauce (a "bad" deed), whereas those who played as Voldemort did exactly the opposite. The study authors suggest a possible explanation for these effects might be related to the lasting influence of total immersion in a virtual environment.
[Thanks to Jose for the tip!]