The dimuon invariant mass spectrum is searched in the range between 5.5 and 14 GeV for a light pseudoscalar Higgs boson a, predicted in a number of new physics models, including the next-to-minimal supersymmetric standard model. The data sample used in the search corresponds to an integrated luminosity of 1.3  fb−1 collected in pp collisions at √s=7  TeV with the CMS detector at the LHC. No excess is observed above the background predictions and upper limits are set on the cross section times branching fraction σ×B(pp→a→μ+μ−) in the range of 1.5–7.5 pb. These results improve on existing bounds on the abb¯ coupling for ma<mΥ(1S) and are the first significant limits for ma>mΥ(3S). Constraints on the supersymmetric parameter space are presented in the context of the next-to-minimal model.l.