The purpose of this study was to unveil Taiwanese junior high school teachers' concerns toward the implementation of Internet-based learning with relations to their perceived Internet self-efficacy. The Stages of Concern (SoC) questionnaire and Internet Self-efficacy (ISS) Survey were utilized to assess teachers' current concerns toward Internet-based learning and their Internet self-efficacy, respectively. A total of 243 junior high school (grade 7 to grade 9) teachers in Taiwan were invited to complete the two above-mentioned instruments. The results show that, first, three distinct teacher clusters were found based on their SoC questionnaire scores via k-means clustering analysis. In addition, teachers with higher Internet self-efficacy showed their concerns toward implementing IBL on higher stages. More specifically, teachers who concerned more in the lower stages tended to possess higher basic Internet self-efficacy. However, only those who concerned more in the higher stages showed higher advanced Internet self-efficacy.