We fabricated NbNx thin-film field emitter arrays by the ion beam assisted deposition technique which can prepare transition-metal nitride thin films at a relatively low temperature of about 500 degrees C. The emitter arrays were fabricated by depositing NbNx thin films on Si cones. The nitrogen composition of the film is controlled by selecting the deposition condition, such as the arrival rate ratio of N to Nb flux. We investigated the influence of the nitrogen composition of the NbNx thin-film field emitter arrays on electron emission characteristics. The emitter arrays with a higher nitrogen composition emitted electrons at a lower voltage and showed more stable emission than those with a lower composition. We compared the emission stability of the NbNx emitters with that of the Si emitters. The emission from the NbN emitter (composition similar to 1.0) was more stable than that from the Si emitter by a factor of 10 in terms of the noise power.