Webster, 33, was indicted in Hamilton County, Ohio, on charges of sexual battery, gross sexual imposition and five counts of unlawful sexual conduct with a minor, The Cincinnati Enquirer reported Thursday.
The indictment alleges Webster assaulted the girl several times from June to December 2009.
The former Bengal was hired in 2010 as the defensive coordinator for the football team at Bellevue High School, the newspaper said.
Webster coached there part of last year, then returned to Florida because of "family issues," Assistant Principal David Eckstein said.
Webster was a linebacker at the University of Miami who signed with the Bengals as a free agent after four seasons with the Tampa Bay Buccaneers.
He played in Cincinnati in just four games over two years, 2005 and 2006, before knee injuries ended his Bengal career.
He played three more years in Denver, the last in 2008, the Enquirer said.