Many scholars have argued that anonymity is the main factor in opinion polarization. In recent studies, scholars have found that being with like-minded others can lead people to adopt extreme opinions. The aim of the current study was to explore how these two online environmental factors impact people to move their opinions toward an extreme position (polarize). In addition to environmental factors, we investigated how an individual trait (i.e., need for approval) influenced people to take pre-existing opinions to an extreme position (polarize). We conducted an online experiment (2 [anonymity vs non-anonymity] by 2 [like-minded others vs different-minded others]) using Amazon Mechanical Turk workers (n = 476). Findings showed that being with like-minded others led individuals to move their opinions toward extremity. Furthermore, we found that among participants who were with like-minded others, those in the anonymous condition were most likely to move their opinions toward an extreme end. However, the need for approval did not play a significant moderating role in this process.