He was 100.
Yadav, who was not keeping well, died at his native place in Triveniganj area of the district bordering Nepal, the sources said.
He is survived by three sons.
Serving as minister in Bihar in 1969 and 1977 under Chief Ministership of Karpoori Thakur, he once represented Saharsa in Lok Sabha and was elected to Bihar Assembly thrice during his long political career.
Bihar Chief Minister Nitish Kumar expressed grief over the death of the leader, describing it as a loss in the field of social and politics and announced a state funeral.
RJD President Lalu Prasad, party's Legislature party leader Abdul Bari Siddiqui and its general secretary Ramkripal Yadav have also condoled the death of Yadav.