Lead-free BNT-based piezoceramics, (1−x)Bi0.5Na0.5TiO3–xBi(Mg0.5Ti0.5)O3 [(1−x)BNT–xBMT] (0.00 ≤ x ≤ 0.06) binary system, were synthesized using a conventional ceramic fabrication method. Effect of Bi(Mg0.5Ti0.5)O3 (BMT) substitution on room temperature (RT) crystal structure, and temperature dependence of electric properties were investigated. The XRD indicates that a pure perovskite phase is formed. The introduction of BMT decreases EC of BNT from 7.3 to 4.0 kV/mm, and increases d33 from 58 pC/N to 110 pC/N for the x = 0.05. The system shows a typical ferroelectric (FE) polarization loop P(E) and butterfly bipolar strain-electric S(E) curve at RT. For the composition of 0.95BNT–0.05BMT antiferroelectric (AFE) phase appears near 80°C, characterized by a constricted P(E) loop and altered bipolar S(E) butterfly, and gradually prevails with increasing temperature. Temperature dependence of dielectric constant shows that TC increases from 310°C for pure BNT to 352°C for the x = 0.05. The results indicate that the piezoelectric properties of BNT have been improved by means of Bi(Mg0.5Ti0.5)O3 substitution.