Although performance of vehicle drivers under fatigue conditions has been investigated in many types of environments, there is insufficient research data about the effects of vibration specifically on levels of mental alertness in seated drivers. In addition to the paucity of research in this area, the study of drowsiness caused by whole body vibration is complex due to several confounding factors (such as lack of sleep, air temperature, health). Hence, we investigated the relationship between whole body vibration and driver drowsiness. A human vibration test setup was designed for this study. Ten subjects were exposed to low frequency sinusoidal and random whole body vibration in multi-axial vibration at 0.3 m/s2 (rms) for 20 minutes. Changes in drowsiness during vibration exposure were measured by recording electroencephalographic signals. Two brainwave spectrums (theta and beta waves) were used for analysis. Exposure to whole body vibration was found to be correlated with a reduction in alertness. Reduction in beta wave and increase in theta wave activity, caused by vibration, were found to be statistically significant. The data presented here quantify for the first time the drowsiness caused by whole body vibration and will help define the threshold limit for safe driving.