Mandal (60) is survived by his wife and two sons.
The JD(U) leader died in his native Dhutha village on way to hospital after a heart attack, the sources said.
Last rites of the leader, who represented Sikti Assembly seat in Araria district in the last term, were performed in his native village this afternoon.
Chief Minister Nitish Kumar condoled the untimely death of Mandal describing the departed leader as a "sensitive personality" who was deeply concerned about development of his region.
State Assembly Speaker Uday Narayan Chaudhary also condoled death of Mandal, while BJP MLA from Sikti, Anandi Prasad Yadav, described him as a great socialist leader who always fought for the rights of the poor.