Context: Existing empirical evidence indicates that loss of alertness associated with mental fatigue is highly correlated with fluctuations in the performance of people carrying out auditory tasks. In software engineering research, mental fatigue may affect the results of study selection (an auditory task) when conducting secondary studies such as systematic literature reviews or systematic mapping studies. However, to date there is no empirical study that reports an in-depth investigation about the relationship between mental fatigue and researchers' selection decisions during study selection process. Objective: The main objective of this paper is to report the design and preliminary results of an investigation about the impact of mental fatigue on the study selection process of secondary studies. Method: We designed and piloted a quasi-experiment. Results: The preliminary results do not indicate that mental fatigue negatively impacts the correctness of selection decision and confidence. However, it is important to note that the preliminary results are only based on six subjects. Conclusion: This paper brings awareness about the role of mental fatigue in the conduction of secondary studies. Although the preliminary results do not indicate any meaningful relationship, we believe that it is worthwhile to continue the research, by adding more subjects, and also revising the design of the reported quasi-experiment. © 2017 ACM.