The private email account was first reported by the Indianapolis Star, which said Pence used it at times to discuss sensitive matters and homeland security issues. The account was hacked last summer, the newspaper added.
During the 2016 presidential campaign, Pence criticised Democratic nominee Hillary Clinton's use of a private email server while she was US secretary of state, saying it endangered national security.
"Similar to previous governors, during his time as Governor of Indiana, Mike Pence maintained a state email account and a personal email account," Pence's office said in a statement.
Indiana law does not prohibit public officials from using personal email accounts, the Star said.
After Pence was hacked in June by a scammer who sent a plea for money to his email contacts, the governor set up a new AOL account, the Star reported.
Pence was chosen by then-Republican candidate Donald Trump as his running mate in July.
Indiana law requires all records dealing with state business to be retained and available for public information requests, the Star reported.
Pence's office said in the statement that he directed outside counsel to review all of his communications as Indiana governor to ensure that state-related emails were being transferred and properly archived by the state.
