The MnTeMoO6 (MTMO) ceramics were prepared by the conventional solid-state ceramic method. It exhibits an orthorhombic structure, belongs to the space group P21212(18) and possesses a favorable combination of dielectric properties (εr =12.3, Q×f =36,000 GHz, and τf =–63 ppm/°C) at microwave frequency. The effects of A-site Mg-substitution on the sintering behavior, phase evolution, and microwave dielectric properties of MTMO ceramics were also investigated. XRD analysis showed that all samples reveal MTMO phase indicating the formation of solid solution in the experimental range. Upon substituting 5 mol. % Mg in the A-site, the relative density of the specimen can be raised from 95.1 % to 97.3 % along with the optimized properties of εr = 13, Q×f = 56,000 GHz and τf = –58.2 ppm/°C, which reveals a 55 % enhancement in the Q×f of the MTMO ceramic. It also renders an excellent chemical compatibility with aluminum metal electrode suggesting that it is a potential candidate for ULTCC applications. •The novel MnTeMoO6 (MTMO) ceramics were prepared by the conventional solid-state ceramic method.•The Mn0.95Mg0.05TeMoO6 ceramic renders excellent dielectric properties with εr = 13, Q×f = 56,000 GHz and τf = –58.2 ppm/oC.•The Mn0.95Mg0.05TeMoO6 present excellent chemical stability with Al making it a potential candidate for ULTCC applications.•The designed a dual-polarized patch antenna for use in the 5G millimeter wave frequency band for the MMTMO ceramic.