Requirements Engineering (RE) process deals with elicitation, analysis, negotiation, validation, management, and documentation of requirements. Several artificial intelligence (AI) based approaches have been proposed to automate RE activities. However, the requirements engineering community still lacks a comprehensive understanding on how expert system are used in RE process. The objectives of this study are (1) to explore the different AI approaches which are employed in requirements engineering, (2) to identify the main phases addressed by these approaches, (3) to identify AI tools that used in RE process, and (4) we tried to find the contributions and the benefits of applying expert system in RE. We found that expert system can partially facilitate the RE process, however no expert system can fully automate the RE process.