Within the framework of effective-mass approximation, exciton states confined in zinc-blende GaN/AlGaN quantum dot (QD) are investigated by a variational approach, including the three-dimensional confinement of electron and hole in the QD and the finite band offset. Numerical results show that both the exciton binding energy and the interband emission energy decrease when QD height (or radius) increases. Our theoretical results are in agreement with the experimental measurements.