A Bronx music teacher has been arrested for allegedly having sex with a 16-year-old student at the school.

Brian Kearins, 33, who works at Lehman HS in Westchester Village, was busted after the girl’s sister discovered e-mails between the two, a source said. The mom alerted the school, and cops arrested Kearins yesterday morning, the source said. He was charged with rape and endangering the welfare of a minor.