Within Dyson-Maleev (DM) transformation and self-consistent mean-field treatment, the Neel order/disorder transition is studied for an antiferromagnetic Heisenberg model which is defined on a square lattice with a nearest neighbour exchange J 1 and a next-nearest neighbour exchange J 2 along only one of the diagonals. It is found that the Neel order may exist up to J 2 /J 1 =0.572, beyond its classically stable regime. This result qualitatively improves that from linear spin-wave theory based on Holstein-Primakoff transformation.