Attorney General Joseph Foster says police were responding to a call from a woman just after 8 a.m. who said her husband had just left their home distraught, suicidal and armed with a shotgun.
Police located his truck at a nearby intersection and the officer approached.
The officer returned fire and the man suffered a single, fatal gunshot wound to the head.
Authorities are withholding the names of those involved at this time. They say the officer involved did not sustain any serious injuries.
An autopsy is scheduled for Thursday.