Lead-free ceramics 0.825NaNbO3–0.175Ba0.6(Bi0.5K0.5)0.4TiO3 + xmol% MnO2 were prepared by an ordinary sintering technique and the effects of MnO2 doping on the structure, dielectric, and piezoelectric properties of the ceramics were studied. The ceramics with perovskite structure are transformed from tetragonal to pseudocubic phases by increasing the doping level of MnO2. After the addition of MnO2, the Curie temperature TC of the ceramics decreases and the ferroelectric–paraelectric phase transition at TC becomes more diffusive. Because of the donor and acceptor doping effects of Mn ions simultaneously, the piezoelectric constant d33, electromechanical coupling coefficient kp, relative permittivity εr, and mechanical quality factor Qm are enhanced considerably after the addition of 1 mol% MnO2. The ceramic with 1 mol% MnO2 doping possesses the optimum piezoelectricity (d33 = 131 pC/N and kp = 21.8%) and relatively high Qm = 627.