In this research, a Graphene based octagonal short-angular circular patch (OSACP) 2×2 multi-input-multi-output (MIMO) antenna is designed for Terahertz (THz) short-range communications. Graphene, as a 2D material, has gained momentum for the realisation of the plasmonic THz antennas due to its unique electromagnetic properties, can fetch the property of surface plasmon polariton (SPP) at THz regime. The graphene layers of thickness 0.01 um have been placed on a Silicon Nitride (Si3N4) substrate of thickness 15 um to increase the efficiency of MIMO antenna. The radiation characteristics of the proposed antenna model are compared to those of a Si3N4 substrate structure based microstrip patch antennas using FDTD technique with a cross-sectional area of 1232 × 1232 um2. It exhibits the return loss (S11) better than -10 dB over the frequency range of 0.259 – 0.324 THz.