Microwave dielectric ceramics are indispensable materials in the field of electronic communication, especially in high-frequency applications. They are widely used in microwave components such as resonators, filters, and oscillators due to their unique dielectric properties, including high relative dielectric constant (ε_r), low dielectric loss, and a temperature coefficient of resonant frequency (τ_f) close to zero. In this study, a Ba(Nd_1/2Nb_1/2)O₃ (BNN) ceramic with a medium dielectric constant was prepared, which was confirmed to be monoclinic system with the space group C12/m1 through X-ray diffraction (XRD) and Rietveld refinement. As the sintering temperature increasing, the samples' densities initially rose, reaching a maximum bulk density (ρ_obs) of 6.32 g/cm³ and a relative density (ρ_rel) of 98% at 1550 ℃ before subsequently decreasing. The sample sintered at 1525 ℃ showed the best microwave dielectric properties: ε_r=38.44, a quality factor Q×f=25400 GHz, and τ_f=-6×10^-6 ℃^-1. It is worth noting that compared to the previously reported value of 11700 GHz, the Q×f value of BNN ceramic in this study increased by 117%, indicating that the microwave dielectric properties of BNN ceramic may have been underestimated due to factors such as testing methods, raw material properties and processing conditions. In addition, a full-dielectric frequency selective surface (FSS) was designed and simulated using this ceramic material, achieving a relative bandwidth of about 23.3%, and demonstrating excellent frequency selection performance. These attributes underscore the potential of BNN ceramics for applications in microwave dielectric ceramic materials and affirm its previously underestimated capabilities, as evidenced by the remarkable performance observed in FSS simulation.