Brain computer interface (BCI) is a system which allows communication between human and machine. BCI systems that control wheelchairs, robotic arms etc. by means of brain activity are being developed to facilitate the daily life of people who can not use their limbs due to damage in motor neurons. In this study, the color, distance and frequency of the visual stimuli are investigated to find out the most prominent brain responses for Steady State Visual Evoked Potential (SSVEP) based BCI systems. 7 stimulation frequencies (15,17,19,21,24,27 and 30Hz) and 3 different colors (white, red, green) were used from 35-60-150 cm distances in order to generate visual stimuli. As a result of examination of 504 EEG segments produced by recording 20 seconds of EEG data for each parameter from 8 subjects using Emotiv EEG headset, 15-24Hz frequency band, 60cm distance and red color were found to be the optimum stimulus parameters.