The study investigated the challenges encountered by mathematics postgraduate students' learning courses via online platforms. An online survey included 31 postgraduate mathematics students. Mean responses and regression analysis were used for data evaluation. The results indicate social-related challenges are the most important factor to learn mathematics in an online platform, although the challenges including accessibility of online learning resource, course nature, online learning skill, and instructor-related challenges are confirmed with a higher mean response. Moreover, a multiple regression analysis has indicated that social and instructor related challenges are significant predictors of students' overall expectation of learning mathematics courses on the online platform. The study concluded that students prefer learning mathematics courses via face-to-face approach over online platforms, and students do not want to extend semester courses with an online approach. From the finding, adapting a blended approach is recommended for a similar situation of the current study.