Specialist William Colton Millay was taken into custody at Joint Base Elmendorf-Richardson on October 28 following a joint espionage investigation conducted by the FBI and Army Counterintelligence special agents, Army spokesman Lt. Col. Bill Coppernoll said.
Coppernoll did not say who Millay, of Owensboro, Kentucky, was suspected of spying for or what sensitive information he may have had access to. He said the investigation was ongoing.
FBI spokesman Special Agent Eric Gonzalez said the case would be tried in military courts.
He also said the arrest was not related to the WikiLeaks case, in which U.S. Army Private Bradley Manning is charged with downloading more than 150,000 diplomatic cables and passing some of them to Wikileaks while working as an intelligence analyst in Iraq.
"It's unrelated, forget WikiLeaks," Gonzalez told Reuters.
A spokesman for the Anchorage Correctional Complex said that Millay was being held there on a federal charge. Millay is assigned to the 164th Military Police Company, 793rd Military Police Battalion, 2nd Engineer Brigade.
"Today's arrest was the result of a close working relationship between the FBI and its military partners in Alaska," Mary Rook, special agent in charge of the FBI in Alaska, said in a brief written statement.
"Through this ongoing partnership, we are better able to protect our nation," Rook said.
Joint Base Elmendorf-Richardson is a combined Army and U.S. Air Force facility near Anchorage.
(Reporting by Yereth Rosen, Writing by Dan Whitcomb; Editing by Greg McCune and Cynthia Johnston)