Double perovskite Ba2FeNbO6 (BFN) ceramics were prepared from the molten-salt synthesized BFN powders. The BFN powders have a cubic structure with Fm3m space group, confirmed by X-ray diffraction patterns. Their average particle sizes increased with the annealing temperature and dwell time whereas decreased with the molten-salt content. X-ray photoemission spectra revealed both Fe2+ and Fe3+ ions present in the BFN powders and oxygen in the forms of lattice oxygen and oxygen vacancies, while niobium was present as Nb5+. The BFN ceramics exhibited significant frequency-dependent dielectric behavior, and two kinds of dielectric relaxor processes were observed. Their activation energies were 0.16 eV and 0.47 eV, respectively. The electron hopping process (between Fe2+ and Fe3+ ions) with the activation energy of 0.16 eV contributes the low-temperature dielectric relaxation process, and an activation energy of 0.47 eV associated with the high-temperature dielectric relaxation is originally from the barrier energy of the thermal motion of the oxygen vacancies. The dielectric relaxation observed at high-temperature region can be explained by Maxwell-Wagner interfacial polarization in the BFN ceramics. M-H plots of the BFN ceramics at different temperatures revealed their antiferromagnetic nature and a weak ferromagnetic behavior at 2 K. The remanent magnetization (M-r) of the BFN ceramics was measured to be 1.75 emu/g at 2 K and coercive field (H-c) as 1.26 kOe. Magnetization splitting was observed at similar to 290 K between the temperature-dependent magnetizations of the BFN ceramics, which were measured under zero field-cooled (ZFC) and field-cooled modes with an external field of 1 kOe. In the ZFC curve, a maximum peak was observed at 14 K, corresponding to the Neel temperature (T-N). The TN of the present BFN ceramics shifts toward low temperature as compared with those prepared by conventional solid-state reaction methods. Such a reduction of the Neel temperature is ascribed to the size effect.