The learner model is a distinctive characteristic of any Adaptive Educational Systems (AES) and Intelligent Tutoring Systems (ITS). The learner model not only is the base of adaptation in AES and ITS systems, but also in some way is used for assessment of learners. Hence, the accuracy of learner model is an important issue. In Open Learner Model (OLM), the learner’s belief can change the learner model. Regarding this problem, it should be determined that how much a system can trust in learner’s belief about his/her model and which characteristics of a learner affect on correctness of learner belief. In this paper we investigate if learner knowledge, background and attention have effect on system trust in Open Learner Modeling. We choose these parameters according to their importance in the learning system. To obtain learner’s knowledge and background multiple choice questions are utilized. The value of attention is estimated by Toulouse-Pieron Test. To evaluate the effect of mentioned characteristics of learner the chi-square distribution is used. The obtained results indicate that the value of learner’s knowledge, background and attention affect on trust value.