We report a comprehensive investigation of the structural, magnetic, and electrical properties in a quasi-two-dimensional planar antiferromagnet , which crystallizes in the rhombohedral structure (space group ) consisting of honeycomb layers of ions. Magnetic susceptibility and heat capacity data reveal a long-range antiferromagnetic ordering of ions at  K. Interestingly, an applied magnetic field induces a dielectric anomaly and an electric polarization at with the polarization proportional to the applied magnetic fields, demonstrating the linear magnetoelectric effect in with a coupling coefficient of 1.67 ps/m. It is interesting to note that the magnetic symmetry associated with the magnetoelectric effect is , which allows all tensor elements of the magnetoelectric susceptibility.