The nature of spin-waves in the quasi-two dimensional spin-1/2 square-lattice Heisenberg system Zn₂VO(PO₄)₂ has been studied. The coexistence of diffuse magnetic scattering and three dimensional antiferromagnetic Bragg peaks in the neutron diffraction pattern below T_N (= 3.75 K), indicates the presence of spin-waves at T< T_N as confirmed by our theoretical calculation using the linear spin-wave theory.