The hosts beat Ethiopia 4-1 on Thursday evening to seal their spot.
Captain Vincent Aboubakar and Karl Toko-Ekambi both scored twice to take the Indomitable Lions through with one group game to spare.
Cameroon had defeated Burkina Faso 2-1 last Sunday in their opening fixture.
But they had to come back from behind at the Olembe Stadium in Yaounde, after Dawa Hotessa gave Ethiopia a shock lead.
The five-time African champions are now well-placed to finish top of Group A.
Their last group game is against Cape Verde, while Burkina Faso take on Ethiopia.
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