Government officials say the commander is resigning after being caught having a physical relationship with a woman who worked for him.
The officials say Maj. Gen. Glenn Rieth (reeth) and the woman were seen by another employee touching each other in Rieth's office. The officials spoke on condition of anonymity because of the sensitive nature of the matter.
The officials say the married Rieth reported the incident to Christie and offered his resignation.
Messages left for Rieth at home and at work Thursday haven't been returned.
Rieth is a member of Christie's Cabinet and a longtime childhood friend and has commanded the National Guard for nearly a decade. He was appointed by Democratic Gov. James McGreevey.