Authorities claim that he intentionally shot 32-year-old Jeff Hall at his Riverside home on Sunday. Authorities aren't talking about a motive.
The boy was handcuffed during Wednesday's brief court hearing but his detention hearing was postponed to May 18. He didn't enter a plea and remains in juvenile custody.
The Associated Press isn't reporting his name because he's a minor.
Relatives who attended the hearing declined to comment.
Hall was a regional leader of the National Socialist Movement, which promotes white separatism. His other four children have been taken into protective custody.