The number of votes polled in Borno has been the subject of controversy as the main opposition candidate, Atiku Abubakar of the Peoples Democratic Party (PDP) raised doubts over the high turnout despite the state's security challenges with a 10-year terrorist insurgency.
"One obvious red flag is the statistical impossibility of states ravaged by the war on terror generating much higher voter turnouts than peaceful states," he said in a statement.
Atiku only polled 71,788 votes in the north-eastern state.
However, in a broadcast, Shettima said it was no surprise that Buhari won in the state as he's always done in the past.
He also said the high turnout was due to the state's ability to mobilise people to the polls despite its security challenges.
He said, "Borno is a Buhari territory from time immemorial. When I contested for the governorship, Buhari got over 90% of the votes in Borno, when he contested under the platform of the CPC (Congress for Progressive Change).
"In 2015, Buhari got the highest percentage of votes nationwide, not in Katsina, not in Kano, not in Sokoto. It was in Borno that Buhari got 97.3%. Candidate Jonathan got a paltry 2.7% in Borno.
"So it is nothing surprising that this time around, Buhari still garnered the highest quantum of votes in terms of percentage. In terms of differential, we are number three.
"Honestly, before we went to the polls, I was thinking we would beat Kano. It is not about the number of registered voters. We have 2.4 million registered voters. It is the ability to mobilise the mass of humanity to come and exercise their franchise.
"Politics goes beyond deliberate distortion of facts, politics goes beyond concoction of lies. It goes beyond impugning on the integrity of others.
"The bottom line is how you are able to mobilise your supporters to come out and vote. This is precisely what we did and this is precisely what we are going to do on Saturday."
Atiku lost the February 23 presidential election to Buhari by 3.9 million votes, but he has rejected the result and vowed to contest it in court, branding it as the worst election in Nigeria's history.