Philosophical mentalism is one of the most important topics in philosophical epistemology, which can be said to have priority over other issues of this science: until the problem of mind and mental existence and the correspondence of mind and object are not explained precisely, no useful result can be obtained regarding the value of perception, science and information; and until we are not sure about the value of information, discussing other issues of philosophy and even other sciences will not be useful and reliable. Therefore, the discussion about mentalism and consequently mental existence and examining its epistemological role are of special importance. Avicenna’s view, as the great Islamic philosopher, about mentalism can inform us about the origin of many differences on the issue of the value of science and information. Using a descriptive-analytical method, this study aims at justifying the external differences around science and information from Avicenna’s viewpoint by examining his theory and rereading his arguments in proving mental existence and its correspondence with objective existence.