In many practical situations, quality of a process or product can well be characterized by a relation between a response variable and one or more explanatory variables. This functional relationship which is commonly referred to as profile has been addressed by many researchers for the case of fixed explanatory variable. However, there are some situations where this assumption may not hold. In this paper, we try to investigate the effect of random explanatory variable on phase II monitoring of simple linear profiles. Average run length criterion is used to evaluate both the in-control and out-of-control performances of the control schemes commonly considered for phase II profile monitoring. The charting performance of the EWMA-3 control scheme has been improved using a novel technique.