We present first-principles calculations on the structural, mechanical, electronic, thermodynamic, lattice dynamic and magnetic properties of RbN in the CsCl, rocksalt (Rs) and zinc-blende (ZB) structures centred on spin-polarised density functional theory (DFT). It was established that in all the three structures, ferromagnetic (FM) state is more stable than the non-magnetic (NM) state. The results show that RbN exhibits half-metallic characteristics at the equilibrium lattice parameters and have small energy gaps of 1.205, 1.092 and 1.364 eV for CsCl, Rs and ZB structures respectively. We find that only the CsCl and Rs structures are mechanically, lattice dynamically and thermodynamically stable. Furthermore, the structures exhibit equal integer magnetic moment of $2 \mu_\rm{B}$ approximately.