Dunn, a former California state senator, was immediately removed from official duties but his employment ends only after the expiration of a 30-day notice period.
The board ordered President Craig Holden and Deputy Executive Director Robert Hawley to assume oversight of the top job for the time being.
There terse announcement gave no explanation for Dunn’s abrupt departure.
He has served as the Bar’s top executive since 2010.
Dunn served as a state senator from OrangeCounty and led the state’s investigation into Enron’s involvement in the 2000-2001 energy crisis.
He was first elected in 1998 and left after a 2006 loss in his run for the Democratic nomination for Controller. Dunn was appointed CEO of the California Medical Association in 2006 before leaving to join the Bar four years later.