"What I've seen is that the level of awareness is very strong, but the biggest risk we have is a certain degree of fatigue," Ismail Ould Cheikh Ahmed said on his second visit to the West African nation.
Ebola has killed more than 3,800 people in Liberia and nearly 9,200 across Liberia, Guinea and Sierra Leone since the first Ebola deaths in rural Guinea in December 2013. All three countries have weak health systems that were ill-prepared for such an epidemic.
Ould Cheikh Ahmed said as one or two cases continue to pop up, people are getting frustrated.
"We call it the bumpy road to zero," he said, warning "the biggest enemy is complacency."
The United States is also preparing to withdraw by the end of April nearly all of its 2,800 troops fighting the outbreak in West Africa, the White House said last week.
A report by Sierra Leone's Auditor General that emerged two weeks ago found that nearly one-third of the money received to fight Ebola, about USD 5.75 million, was spent without saving the necessary receipts and invoices.
The list released Tuesday included district medical doctors, the coordinator of the National Ebola Response, a former permanent secretary in the Ministry of Health and Sanitation, other government officials, private contractors and business people.