Freshman Rep. Rep. Markwayne Mullin (R-Okla.) and his family have received death threats, an aide said Saturday.

In a statement, chief of staff Karl Ahlgren said the threats were being investigated by federal authorities, who consider it "a serious matter due to the content and nature of the threatening letters which were received."

U.S. Capitol Police Officer Shennell Antrobus told reporters that an investigation is underway.

Mullin was elected to Congress with little political experience, winning an eastern Oklahoma seat formerly held by Rep. Dan Boren (D). While Democrats have a registration edge in the district, it is deeply conservative and tends to go Republican on the national level. He was one of 67 House Republicans who voted against a federal aid package for victims of Hurricane Sandy.

Mullin left college at 20 to run his family's plumbing business. A member of the Cherokee Nation, he is one of only two Native Americans in Congress. The other is fellow Oklahoma Republican Rep. Tom Cole.