Nowadays, complex systems represent research topics to a variety of sciences and professional practice methods. In the social sciences field, the main objective of the complexity studies would be to explain the interactions between the members of a social system (economic, etc.). To conduct the internal audit activity in terms of economy, efficiency and effectiveness requires a functional structure of internal audit and a set of achieving objectives. The study presents the audit engagement and the factors that disturb the execution of audit plan. In terms of low level interactions from the complex system theory, this will lead to different kind of phenomena. Communicating the results of work carried out in an objective and exhaustive manner, by presenting convincing and pertinent arguments contributes to improving activities in companies through internal audit reports. The company's decision to fulfil its objectives through a systematic and methodical approach based on risk management, control and management processes can be changed by a nonlinear interaction.