Self-explaining, which asks students to generate explanations while reading a text, is a self-constructive activity and is helpful for students’ learning. The studies also revealed that human tutor’s prompts promote students’ self-explanations. However, most studies of self-explaining focus on spoken self-explanations. This study investigates the effects of content-free computer support on self-explaining, including a full-text reading and typing self-explaining computer interface and content-free prompts. The results showed that typing self-explaining, particularly when prompted, makes students perform better in applying target knowledge to similar problem. In addition, this study uses the computer as a learning companion to provide prompts without understanding the content of students’ self-explanations. The results showed that content-free and content-related prompts both make students perform better in applying target knowledge to similar problem.