A method of forming a positive resist composition of the present invention includes a step (I) of passing a positive resist composition, which is obtained by dissolving a resin component (A) that displays increased alkali solubility under the action of acid and an acid generator component (B) that generates acid upon exposure in an organic solvent (S), through a filter (f1) equipped with a nylon membrane, wherein the resin component (A) is a copolymer containing at least two structural units obtained by polymerizing at least one monomer in the presence of acid. According to the present invention, it is possible to provide a method of producing a positive resist composition, a positive resist composition, and a method of forming a resist pattern that are capable of forming a resist pattern with reduced levels of both bridge-type defects and reprecipitation-type defects.