The man died after arriving at Lagos airport on Tuesday, in the first Ebola case in Africa's most
Surveillance has been stepped up at all "airports, seaports and land borders", says Health Minister Onyebuchi Chukwu.
Since February, more than 660 people have died of Ebola in West Africa - the world's deadliest outbreak to date.
It began in southern Guinea and spread to Liberia and Sierra Leone.
The Liberian man collapsed on arrival in Lagos last Sunday. He was taken from the airport to hospital,
where he was put in quarantine.
Officials have identified the 40-year-old man as an employee of the Liberian government.
Mr Chukwu confirmed that the other passengers on board the flight had been traced and were being monitored.
The patient had "avoided contact with the general public" between the airport and the hospital, he said.
Health specialists have been deployed at all entry points into the country, he added.
The virus, which kills up to 90% of those infected, spreads through contact with an infected person's
Patients have a better chance of survival if they receive treatment early.