Na0.5Bi0.5TiO3-based ceramics have been paid great attention as Pb-free piezoelectric and electrical energy storage materials. Here, adding 10 mol% BiFeO3 in Na0.5Bi0.5TiO3–SrTiO3 binary system, 0.5Na0.5Bi0.5TiO3–0.4SrTiO3–0.1BiFeO3 ceramics were prepared by a conventional solid-state reaction method. Dielectric measurements reflected a near-plateau dielectric response at high temperature, e.g., the mid-dielectric permittivity of 2052 with the variation within ±10% from 57 to 371 °C and within ±15% from 54 to 371 °C for the ceramic sintered at 1100 °C. At a moderate electric field of 70 kV/cm, a capacitor made by the ceramic has an electrical energy storage density of 0.95 J/cm3, while the polarization has yet saturated at the moderate electric field. These results suggest that 0.5Na0.5Bi0.5TiO3–0.4SrTiO3–0.1BiFeO3 ceramic is a promising novel material with thermally stable dielectric permittivity and high electrical energy storage property for applications in high-temperature electronics.