The thermodynamic properties of some symmetric hard core Yukawa mixtures with positively and negatively nonadditive diameters are studied by molecular dynamics (MD) simulation, and the results compared with the predictions of the mean spherical approximation (MSA). MSA results for the compressibility factors are obtained by taking as reference the semiempirical equation of state proposed by Gazzillo and Pastore for symmetric nonadditive hard sphere fluids. Our calculations show that the "exact" computer simulation data are, in general, closely approximated by the MSA energy route to the thermodynamic properties. For the largest positive nonadditivity considered in this paper, some discrepancies appear between the compressibility factors obtained by MD and the MSA, but it is shown that the origin of the discrepancies lies in the hard core part of the compressibility factor rather than in the MSA theory of liquids.