This study examined epistemic metacognition as a reflective activity about knowledge and knowing in the context of online information searching on the Web, and whether it was related to prior knowledge on the topic, study approach, and domain-specific beliefs about science. In addition, we investigated whether Internet-based learning was influenced by epistemic metacognition and the individual differences examined. Seventy 8th grade students were interviewed retrospectively after searching for online information about the scientifically controversial topic of dinosaur extinction. Both qualitative and quantitative analyses were performed. Findings showed that participants expressed reflections about the simplicity/complexity, certainty/uncertainty, source, and justification of knowledge at different levels of sophistication, according to three patterns of epistemic metacognition. Prior knowledge was not related to epistemic metacognition in the search context, while study approach and epistemic beliefs about science were associated significantly, although modestly, with aspects of online knowledge evaluation. Moreover, findings revealed that Internet-based learning was influenced by overall science-related epistemic beliefs. Learning from Internet sources was also affected by study approach and epistemic reflections about the justification of online knowledge, as well as by the interaction between beliefs about the justification of scientific knowledge and beliefs about the justification of the knowledge accessed concerning the topic.