It is well known that short run cost functions of firms are convex func-\ntions when production functions are concave. Average cost minimization prob-\nlems have been studied in the literature. However, it seems that less attention\nso far has been paid to properties of the average cost functions and numerical methods for solving the average cost minimization problem. Aim of this paper is to fulfill\nthis gap. First, we show that average cost functions are pseudoconvex. Second,\nwe develop an algorithm for solving the average cost minimization problem. We\nimplement the algorithm in the case of some companies of Mongolia.