 The main objective of this study is to analyze the effect of a short self-administered Motivational Online Intervention MOI using pedometers to increase PA levels primary outcome and to change different theoretical constructs related to the PA behavior positive decisional balance, self-efficacy, processes of change, stage of change, and enjoyment secondary outcomes in a sample of sedentary students after 3-weeks intervention post and after 3-months follow-up. It will be compared three conditions: MOIPEDOMETER condition access to a MOI and the use of a pedometer of new generation; MOI condition access to a MOI and the use of blinded pedometer; and CONTROL condition the use of a blinded pedometer. Hence, two conditions will include components of the Transtheoretical Model of Change in the intervention, such as the facilitation of the decisional balance, the increase of the self-efficacy, and the use of experiential and behavioral processes of change e.g., consciousness raising, counterconditioning, reinforcement management, stimulus control, but only one of these condition will receive the feedback of the pedometer that will allow self-monitoring the behavior. 