WHO representative Rui Gama Vaz, speaking in the capital Abuja, said it was a "spectacular success story".
Nigeria won praise for its swift response after a Liberian diplomat brought the disease there in July.
The outbreak has killed more than 4,500 people in West Africa, mostly in Liberia, Guinea, and Sierra Leone.
An estimated 70% of those infected have died in those countries.
The WHO officially declared Senegal Ebola-free on Friday.
Meanwhile, European Union foreign ministers are meeting in Luxembourg to discuss how to strengthen their response to the threat posed by Ebola.
Speaking on the sidelines, French Foreign Minister Laurent Fabius said he expected the meeting to appoint a co-ordinator to galvanise the EU's response to the epidemic.
"My colleagues are unanimous in saying that this idea of a European co-ordinator for the fight against Ebola is a good idea. The name will be chosen in the coming days. I think it's a very important step."
European countries have committed more than 500m euros (£400m; $600m) but the UK is pressing to double that amount.
