Two dropped points leave Cameroon vulnerable in a tough group where their major rivals Senegal went to the top of the Group E standings after hammering Mauritius 7-0 at home.
Cameroon's failure to win in new coach Javier Clemente's home debut was the only surprise result among the 11 Nations Cup qualifiers played on Saturday.
They fell behind to a 37th minute goal from defender Herita Ilunga, who then missed a similar chance to double the lead just one minute later.
Congo gifted Cameroon an equaliser in the 54th minute when Eric Nkulukuta sliced an attempted clearance into his own net.
The home side started the game without midfielder Stephane Mbia and striker Eric Choupo Moting, who were both suffering from heat stroke after wilting in the sweltering temperatures in the days leading up to the match.
Papiss Demba Cisse grabbed a hat-trick and Mamadou Niang scored twice in Senegal's rout, which takes to 11 the number of goals they have scored in two qualifying matches to date.
Malawi were also among the goals in a 6-2 home win over Chad that put them second in Group K while Benin, Morocco, Mozambique and Ivory Coast all won away from home.
The Ivorians, without the Chelsea pairing of Didier Drogba and Salomon Kalou, battled out a narrow 1-0 in Burundi with Christian Koffi Ndri, otherwise known as Romaric, netting a first-half winner.
Morocco bounced back from a draw in last month's opening qualifying game in Group D to beat Tanzania 1-0 with Mounir El Hamdaoui, set up by a header from Marouane Chamakh, scoring two minutes before halftime.
Benin beat Rwanda 3-0 in Kigali while Mozambique won with the only goal of the game in the Comoros Islands.
Burkina Faso made a belated start to their qualifying campaign with a 3-1 home win over the Gambia while 2010 Nations Cup hosts Angola got their first points with a 1-0 victory over Guinea Bissau.
Saturday's win in Luanda was secured with a 22nd minute penalty converted by Gilberto.
A further 10 qualifying matches are being played on Sunday.
The 11 group winners, plus the top three runners-up qualify for the finals, which are being co-hosted by Equatorial Guinea and Gabon.
