From Wikipedia, on Posse Comitatus:
“The Act only specifically applies to the United States Army and, as amended in 1956, the United States Air Force
... the Act does not explicitly mention the United States Navy and the United States Marine Corps
... The Act does not apply to the Army National Guard and the Air National Guard under state authority from acting in a law enforcement capacity within its home state or in an adjacent state if invited by that state’s governor.
The United States Coast Guard, which operates under the Department of Homeland Security, is not covered by the Posse Comitatus Act either”
My understanding is that the National Guard is, when activated, just another active duty arm of whatever service it is a part of.