Humans apply a large variety of deception forms in their communicative acts; they are not necessarily ‘uncooperative’ in doing so, as they may even deceive for the benefit of their interlocutors [2,3]. Deception may be active or passive, according to whether the Speaker does something or not, to achieve his goal. It may be applied directly to the deception object p or may indirectly influence it through some ‘deception medium’ q that may be a cause, an effect or a diverting cause or effect of p. In this short paper, we examine how deception may be simulated if mental states are represented as belief networks and various weights are attached to beliefs.