MnO2 doped (Na0.82 K0.18)0.5Bi0.5TiO3 lead-free piezoelectric ceramics were prepared by conventional solid-state reaction process and the effect of MnO2 addition on the pyroelectric, piezoelectric and dielectric properties were studied. The experiment results showed that the pyroelectric, piezoelectric, and dielectric properties strongly depended on MnO2 addition in the (Na0.82 K0.18)0.5Bi0.5TiO3 ceramics. Excellent electrical properties were obtained in (Na0.82 K0.18)0.5Bi0.5TiO3 with 0.8 mol% MnO2. The large dielectric loss of pure BNT ceramics was significantly reduced, the piezoelectric constant was improved, and it also showed excellent pyroelectric properties when compared with other lead free ceramics, with pyroelectric coefficient p = 17 × 10−4 C/m2K and figure of merit Fd = 6.56 × 10−5 Pa−0.5. With these outstanding pyroelectric properties, the 0.8 mol% MnO2 doped (Na0.82 K0.18)0.5Bi0.5TiO3 ceramic can be a promising material for pyroelectric sensor applications in future.