Since augmented reality (AR) has been increasingly applied in education recently, the investigation of students' learning experiences with AR could be helpful for educators to implement AR learning. With a quantitative survey using three questionnaires, this study explored the relationships among 153 students' perceived cognitive load, motivation, and attitudes of perceived control, perceived usefulness, behaviour of learning, and behaviour of AR learning, when they engaged in an AR book reading activity. The results indicated that, in general, the students perceived less cognitive load, stronger motivation, and more positive attitudes towards the experiences when reading an AR book. However, dissimilar to past studies, the perceptions of low level cognitive load cannot be guaranteed to lead to positive intentions to learn. Interestingly, motivation mediated the relationships between the students' perceived cognitive load and behavioural intention to learn. Only when the students' perceptions of motivational factors such as attention or confidence were significant did the perceived usefulness and cognitive load play a role in their behavioural intentions to take part in future AR learning. The findings of this study may provide insights for future AR-related studies to explore the role of cognitive load in learning performance with consideration of motivational factors.