By Brendan O'Brien

MILWAUKEE (Reuters) - An ex-girlfriend of the gunman who killed six worshippers at a Sikh temple in Wisconsin has been arrested and faces a weapon charge, investigators announced on Tuesday.

A charge of being a felon in possession of a firearm will be sought through the Milwaukee County District Attorney against Misty M. Cook, 31, according to a brief statement released by the South Milwaukee Police Department.

The statement did not say where or when Cook was arrested.

On Sunday, Wade Michael Page, her ex-boyfriend, gunned down six members of the Sikh Temple of Wisconsin in Oak Creek, south of Milwaukee, before a police officer killed him. The 40-year-old U.S. Army veteran also wounded four people, including a police officer.

Federal authorities said they were treating the attack as a possible act of domestic terrorism. Page was involved in white supremacist groups and was a member of skinhead rock bands.

Cook and Page lived together in South Milwaukee before breaking up in June, according to neighbors.

(Editing by Corrie MacLaggan and Lisa Shumaker)