Due to the rapid development of information technology, web-based learning has become a dominant trend. That is, learners can often learn anytime and anywhere without being restricted by time and space. Autonomic learning primarily occurs in web-based learning environments, and self-regulated learning (SRL) is key to autonomic learning performance. Moreover, sustained attention to web-based learning activities can be challenging for students. Therefore, a web-based reading annotation system with an attention-based self-regulated learning mechanism (ASRLM), which is based on brainwave detection, is designed to enhance the sustained attention of learners while reading annotated English texts online, and thereby promote online reading performance. In total, 126 Grade 7 students in four classes at a junior high school in New Taipei City, Taiwan, are the participants. Among the four classes, two classes are randomly distributed to the experimental group and the other two classes are randomly distributed to the control group. The experimental group utilizes the ASRLM to support their reading of annotated English texts online, whereas the control group is not supported by the ASRLM while reading annotated English texts online. Experimental results show that sustained attention and reading comprehension of the experimental group are better than those of the control group. Moreover, the web-based reading system with ASRLM support promotes the sustained attention and reading comprehension of female learners more than those of male learners while reading annotated English texts online. Additionally, learners with high-SRL ability in the experimental group have better sustained attention and reading comprehension than those learners with low-SRL ability. Furthermore, the sustained attention and reading comprehension of the experimental group are strongly correlated, and the duration of sustained attention strongly predicts their reading comprehension performance.