Research on causal mechanisms and dynamic processes of relaxation phenomena in a Reversed Field Pinch (RFP) plasma is reviewed in relation to toroidal flux generation, anomalous ion heating and loop voltage. The anomalous transport related to MHD fluctuations is briefly mentioned. Recent development of three dimensional, non-linear resistive MHD simulations and detailed measurements in RFP experiments reveal the behavior of MHD activity of RFP plasma more clearly.