Kamil Kopunek's first goal for the national side gave Slovakia the lead in the sixth minute.
The Slovaks claimed a second goal early in the second half but the referee ruled that centre-forward Stanislav Sestak's shot had not crossed the goal line.
Cameroon, missing Inter Milan striker Samuel Eto'o, equalised with a late strike from midfielder Eyong Enoh.
On Friday, captain Eto'o threatened to not go to the World Cup in South Africa after former international Roger Milla criticised his performances for the national side.
NEWS:Eto'o threaten to skip World Cup
"I still have a few days to think about it but I will see if my participation is important because I don't need this in my career," Eto'o told French television channel Canal Plus Sport.
Slovakia play another friendly in Bratislava, against Costa Rica next Saturday, before flying to South Africa. Cameroon meet Portugal in a friendly in Covilha on Tuesday.
Cameroon are drawn in Group E for the June 11 to July 11 tournament, with the Netherlands, Denmark and Japan, while Slovakia face Italy, New Zealand and Paraguay in Group F.
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