The Essex outfit have won two of their opening nine league matches, most recently falling to a 6-2 defeat at home to Hampton & Richmond Borough.
O’Hara, 34, took the reigns in September last year before guiding Ricay to a 17th place finish in Vanarama National League South.
The club confirmed his assistant Paul Konchesky would also be leaving New Lodge.
In a brief statement, the club said: “The Board would like to announce, that following discussions earlier today, Billericay Town FC, Jamie O’Hara and Paul Konchesky have decided to part company.
“The club would like to thank them both for their contribution and we wish them nothing but the very best.
“In the next day or so the club will announce the interim management arrangement and will start a comprehensive search for the new management team and we will be accepting applications”.