One of the reasons for students’ reluctance to study and succeed in mathematics is that they may not be motivated to learn. This study examined fresh senior high school (SHS) students’ achievement motivation levels and its correlate to self-efficacy towards core mathematics. The study adopted descriptive research design involving a random sample of 314 fresh students in three SHSs in a low performing district in Ghana. The achievement motive scale and the new general self-efficacy scale were adapted and used for data collection. Data were analyzed using descriptive statistics, independent t-test, one-way analysis of variance and Spearman rank correlation. The results indicated that the students’ achievement motivation levels in dimensions of striving to achieve learning targets, participation in lessons, willingness to work and maintaining positive study habits towards mathematics were quite high. Furthermore, the students’ achievement motivation levels did not differ by gender, type of junior high school attended and boarding status. However, the students’ achievement motivation levels varied across the five programs of study. The study also found a moderately positive significant correlation between students’ achievement motivation and self-efficacy beliefs. The study concludes that the fresh students in this study are highly motivated and believe they can succeed in their study. The study recommends that mathematics teachers should guide these fresh students to set realistic short-long term learning targets to facilitate higher achievement in mathematics. Mathematics teachers should try to first gauge the achievement motivation of the fresh students for high school mathematics for appropriate pedagogical decisions.