Energy-storage properties of 0.89Bi0.5Na0.5TiO3-0.06BaTiO3-0.05K0.5Na0.5NbO3 (0.89BNT-0.06BT-0.05KNN) lead-free ceramics were first investigated. Measurements of dielectric properties together with switching current curves indicate a rather diffuse ferroelectric (FE) to anti-ferroelectric (AFE) phase transition when heating from 20 degrees C to 90 degrees C. The energy density (W), which was calculated from P-E hysteresis loops, increases linearly with the external electric field when E exceeds AFE-FE transition field. W is independent of temperature and frequency, and maintains around 0.59 J/cm3 under 5.6 kV/mm in the stable AFE phase region. These properties indicate that 0.89BNT-0.06BT-0.05KNN ceramics might be a promising lead-free AFE material for energy-storage capacitor application.