In mobile augmented reality (MAR) games, learning by doing is important to supplement the theoretical knowledge with practical exercise in order to maximize the learning outcome. However, in many fields, the users are not able to apply their knowledge in practical ways, despite having achieved a good understanding of the theoretical fundamentals and this is even more important to adult learners. The aim of this research is to examine young, middle-aged and elderly adults’ opinions about the location-based MAR game Ingress, by applying John Keller’s “ARCS learning motivation model” (Attention, Relevance, Confidence and Satisfaction). The users’ responses to closed questions related to Ingress were collected from 45 adult players aged 20–60 from Greece and were subsequently analyzed by means of pre- and post-quantitative measures of the four ARCS factors. The results show that: (a) game training improves all the factors of ARCS, primarily attention and satisfaction; (b) the responses of young people (20–35) agree more with those of elderly adults (>52) than with those of the intermediate age group of 36–51. Our findings, therefore, highlight the potential and the applicability of the ARCS model in MAR games.