In the present study it was investigated whether high school students are spontaneously able to reflect epistemologically during online searching for information about a controversial topic. In addition, we examined whether activating epistemic beliefs is related to individual characteristics, such as prior knowledge of the topic and argumentative reasoning skill; also whether learning from the Web is influenced by epistemic beliefs in action and the ability to detect fallacies in arguments. The participants (N = 64) were students of Grade 13, who were asked to think aloud during navigation. Qualitative and quantitative analyses were performed. Findings reveal that most participants spontaneously activated beliefs about all four dimensions identified in the literature, that is, about the simplicity/complexity, certainty/uncertainty, justification, and source of knowledge, at different levels of sophistication. Most epistemic reflections were about the source of knowledge. Two patterns of contextualized epistemic beliefs emerged and significantly influenced learning from the Web, which was also affected by participants' ability to identify argumentative fallacies. (Contains 5 tables and 1 figure.)