Online videos are a popular means of imparting education. This study investigated the effects of different questioning strategies used in online videos on learners' attention levels, as well as the mediating effect of attention levels on the relationship between questioning strategies and learning performance. One hundred students from a Chinese University were randomly assigned videos with one of five questioning strategies: the pre-leading questioning (PLQ), middle-enhancing questioning (MEQ), and post-assessment questioning (PAQ) strategies as well as a combination of PLQ and MEQ and PLQ and PAQ. By using an electroencephalogram (EEG) to measure the learners' brainwaves, this study found that embedding questions in online videos could increase learners' attention levels. The results demonstrated that learners exposed to a combination of the two questioning strategies paid better attention than those exposed to a single strategy. Furthermore, attention level was found to be the only mediator in the relationship between the PLQ + MEQ strategy and learning performance while it played a suppressive role in the relationship between the PLQ + PAQ strategy and learning performance. These findings have significant implications for education. Instructors should design questions for online videos based on their teaching objectives at a given stage and consider the potentially negative consequences of other factors (such as cognitive load) when using multiple questioning strategies in the same video.