Magnetic and magneto-optical properties of cobalt nanoparticles (Co-NPs) dispersed in a transparent dielectric SiO2 and semiconductor ZnO matrices have been investigated. Field and temperature dependences of the samples magnetization showed the typical behavior of an ensemble of superparamagnetic particles with a blocking temperature near and below room temperature. The spectroscopy of magnetic circular dichroism (MCD) in the visible and near-infrared light ranges has revealed a significant difference between the behavior of the Co-NPs and a solid Co film. It has been found that the MCD spectrum shape for the Co-NPs does not depend on the matrix type. The room temperature magneto-optical activity of the Co-NPs in the different matrices has been estimated as an indicator for practical applications.