Bigdata and IoT technologies are developing rapidly. Accordingly, consideration of network security is also emphasized, and efficient intrusion detection technology is required for detecting increasingly sophisticated network attacks. In this study, we propose an efficient network anomaly detection method based on ensemble and unsupervised learning. The proposed model is built by training an autoencoder, a representative unsupervised deep learning model, using only normal network traffic data. The anomaly score of the detection target data is derived by ensemble the reconstruction loss and the Mahalanobis distances for each layer output of the trained autoencoder. By applying a threshold to this score, network anomaly traffic can be efficiently detected. To evaluate the proposed model, we applied our method to UNSW-NB15 dataset. The results show that the overall performance of the proposed method is superior to those of the model using only the reconstruction loss of the autoencoder and the model applying the Mahalanobis distance to the raw data.