Nigerian voters go to the polls on Saturday to elect governors and lawmakers in 29 of the nation's 36 states.
The vote comes two weeks after presidential and national assembly elections in which Buhari was elected for a second term after defeating Atiku Abubakar, the main opposition candidate.
The vote was marred by violence with at least 53 people killed across Nigeria.
In a statement in Abuja, the nation's capital, Buhari urged Nigerians "to turn out in large numbers to exercise their civic rights."
He said: "With the presidential poll behind us, let us not become complacent and fail to vote in the gubernatorial poll."
He said the polls were as important for good governance as the presidential and the national assembly elections.
"Indeed, governance at the state level is closer to us, and should touch our lives more directly. That is why it is vital for us to participate in the choice of who governs us at the state levels," he said.
"I, therefore, urge you to troop out massively on Saturday."
The Nigerian leader also urged voters to "avoid all deviant behaviours like ballot stuffing, ballot snatching, and any other action that does not conform with best electoral practices."
And he appealed to Nigerians not to allow themselves "to be used to cause violence or to break the law or otherwise disturb the peace."