A three-dimensional electromagnetic field analysis model was developed to estimate ac losses in high-temperature superconductor (HTS) coils composing superferric magnets for rapid-cycling synchrotrons. The influence of magnetized iron yokes in the superferric magnets on distributions of magnetic flux density in HTS coils was considered as externally applied magnetic flux density to HTS coils in the analysis model. We carried out the ac loss calculations using the models for two superferric magnets having different iron core and HTS coil geometries. The ac loss density distribution in the HTS coils and overall ac losses of the superferric magnets were compared.