Carter was assigned a government account after he became defense secretary in February 2015. The use of a personal email account for government work violates US Defense Department rules, adopted in 2012.
"After reviewing his email practices earlier this year, the secretary believes that his previous, occasional use of personal email for work-related business…was a mistake," Carter’s spokesperson Peter Cook said in a Wednesday statement, as quoted by The New York Times.
According to Cook, Carter has stopped using his personal email and has limited the use of email altogether.
It is not clear exactly how many work-related emails Carter has sent and received from his personal account.
The New York Times cited a former aide to Carter as saying that the defense secretary used a personal email, in violation of the Defense Department rules, with a high frequency that was alarming to his staff.
The revelations are reminiscent of Hillary Clinton using a personal email for official government business during her tenure as secretary of state. Clinton’s use of a personal email account for work was publicly revealed in March.