In this paper, room-temperature blue cathodoluminescence from ZnO:Er thin films has been studied using different electron beam currents. The ZnO:Er thin films used in our experiment were prepared by simultaneous evaporation from ZnO and Er sources. The X-ray diffraction spectra showed that the thin films had a strong preferential c-axis (0002) orientation with a hexagonal crystalline structure. The blue light emission at 455 nm originating from the intra-4f shell transition (F-4(5/2) --> I-4(15/2)) in Er3+ ions was observed at room temperature. This is because many Er ions in the ground states resonantly absorb the energy from the emission related to deep-level defects and cathode ray, then fill in the H-2(11/2) state, the non-radiative relaxation rates from the F-4(5/2) state to the H-2(11/2) state are completely suppressed. The non-linear dependence of the cathodoluminescence intensity on the electron beam current showed a blue light emission above the threshold electron beam current (I-th) of 0.6 muA, which was attributed to the phonon bottleneck effect. Furthermore, the near infrared luminescence at 1.54 mum was obtained at room temperature.