The popstar said the restraining was needed after his little brother "threatened to kill" Nick's pregnant wife, according to the BBC.
The singer, 39, said the legal move came "in light of Aaron's increasingly alarming behaviour".
Aaron, 31, must now stay 30 metres away from Nick, his family and their Las Vegas home.
In response, Aaron Carter said he was "astounded" by the accusations.
"I do not wish harm to anyone, especially my family," he said.
Nick Carter said: "After careful consideration, my sister Angel and I regret that we were required to seek a restraining order against our brother Aaron.
"In light of Aaron's increasingly alarming behaviour and his recent confessions that he harbours thoughts and intentions of killing my pregnant wife and unborn child, we were left with no choice but to take every measure possible to protect ourselves and our family.
"We love our brother and truly hope he gets the proper treatment he needs before any harm comes to himself or anyone else."