Computer-aided detection (CAD) systems help to radiology experts in mass detection using image processing techniques. This study aims to realize mass detection process on brain MRI (Magnetic Resonance Imaging) images. This paper describes the CAD system that is based on histogram equalization and morphological image processing techniques. The processes are carried out through 125 MR images which are taken from 11 people that are 8 people with tumors, 3 people without tumors. In classification stage which is the last stage of the computer-aided detection systems, 6 classification algorithms are tested in the RapidMiner program, and these algorithms are compared with each other to show CAD system accuracy.