Behr first appeared on the small screen as a guest in 1994 episodes of "Step By Step" (ABC). The following year he gained notice as Tyler on Showtime's "Sherman Oaks", a series parodying cinema-verite documentaries examining the workings of the American family. In 1996 he had a supporting role in Fox's telefilm "Alien Nation: Millennium", playing a sinister human teen who pretends to have an interest in Tenctonese culture in a bid to seduce a young alien woman, going so far as to paint spots on himself to mimic alien markings. He continued to appear in guest roles, featured on series including CBS' Navy legal drama "JAG" and ABC's short-lived detective remake "Cracker". In 1998 he took on his own short-lived series, starring as Dempsey Easton, a fiercely competitive middle distance runner enrolled in an elite university athletic program, in "Push" (ABC). Easton turns to steroids to make the grade, and while Behr proved his acting capabilities in the show, suitably evoking the character's moral ambiguity, the series wasn't around long enough to fulfill the young performer's promise.
Behr made his film debut with a small part in "Pleasantville" (1998) before taking on a challenging starring role as a young gay man unexpectedly reunited with his estranged brothers and father under tense and potentially dangerous circumstances in Victor Salva's small-scale independent "Rites of Passage" (1999). Behr returned to the big screen in 2001 playing the supporting role of an aspiring fisherman in the screen adaptation of "The Shipping News". The actor's profile got a big boost when he appeared as Sarah Michelle Gellar's boyfriend in the surprise horror hit "The Grudge" (2004).