Arihira was the son of FUJIWARA no Ariyori, who was Tajima no kuni no suke (the assistant governor of Tajima Province) and the child of FUJIWARA no Yamakage (Chunagon, or vice-councilor of state), but a theory says Arihira was in real the child of Nyomu, who was Daisozu (the Buddhist priest in the second highest position) and the younger brother of Ariyori.
但馬国介藤原有頼（中納言藤原山蔭の子）の子であるが、実は有頼の弟・大僧都如無の子という説もある。