Buhari's speech came at an event on Sept. 8 which called for an end to "dishonesty, indolence, unbridled corruption and widespread impunity" in Nigeria as part of his "Change Begins With Me" campaign.
Adeola Akinremi, a columnist at Nigeria's THISDAY newspaper, noticed the similarities and called Buhari "unethical" for his unauthorized use of Obama's 2008 victory speech.
"It is immoral to plagiarize other people's work, but even worse to use dishonesty to launch a campaign about honesty," he said.
Buhari's office said the speeches were "too close to be passed as coincidence."
His office also said the fault lies with an "overzealous staff" member.
"President Buhari urges Nigerians to look beyond this incident and focus on the message of change," Buhari's spokesman tweeted on Friday.
10. President Buhari urges Nigerians to look beyond this incident and focus on the message of change...— Garba Shehu (@GarShehu) September 16, 2016