Odion Ighalo, John Mikel Obi, Victor Moses and Kelechi Iheanacho were all on target for Nigeria in their victory.
The win means the Super Eagles top Group B on nine points while Cameroon have just two after three matches.
Zambia and Algeria both have a point each and they play their third match, against one another, on Saturday in Lusaka.
Nigeria took the lead on 29 minutes when Ighalo latched onto a ball over the top from captain John Mikel Obi before drilling home.
Ighalo was then booked for revealing a T-shirt in support of his international colleague Carl Ikeme, who is suffering from leukaemia.
Just before half-time, a corner from Moses was turned in by his former Chelsea team-mate Mikel Obi as he stabbed into the roof of the net from close range.
Moses scored the third in the 55th minute after an exchange of passes with Moses Simon.
The rout for Cameroon, who won the Africa Cup of Nations in February, was completed when Leicester City striker Kelechi Iheanacho stooped to head home a cross from Ogenyi Onazi with 14 minutes left.
culled from bbc