This paper is a part of MUSAMAT Project which demonstrates the empirical evidence relating to the attitudes of Finnish pre-service primary school class teachers toward the integration of music in mathematics lessons. Framed within the Theory of Planned Behaviour (TPB) and Dweck’s Mindset Theory, this study addressed three research questions: 1) What is the relationship between teachers’ self-efficacy in using music and their attitudes toward integrating music into mathematics lessons? 2) To what extent does the teachers’ musical background and hobbies relate to their attitudes toward integrating music into mathematics lessons? 3) Is the duration of musical background and hobby practice associated with Finnish pre-service primary school class teachers’ fixed mindset regarding their musical ability? A survey questionnaire developed by Prof. Minna Huotilainen was employed in this quantitative study, where 114 Finnish pre-service class teachers participated. Synthesizing the participants’ attitude and mindset towards using music in their mathematics lessons, the study highlights three main findings. Firstly, there is a moderate positive relation between the teachers’ attitude and their pedagogical self-efficacy toward implementing music in their mathematics lessons. Secondly, teachers’ personal musical background such as formal musical education or training, and hobbies do not demonstrate significant relation towards teachers’ positive attitude in using music as a pedagogical tool in their mathematical classes. Finally, the result provides evidence that teachers’ mindset regarding using music in their mathematics classroom has a significant association with the duration of their previous musical background and hobbies practice. Teachers who have less duration of musical background and hobby practices demonstrated fixed mindset. The findings of the research will contribute to the progression of primary level interdisciplinary education in Finland by providing perceptions about the factors that influence teachers’ willingness and barriers to implement music as a pedagogical tool in their mathematics lesson. Furthermore, the study will support the educational policymakers to design strategies in teacher education that promote STEAM teaching practices aligning with Finnish National Core Curriculum.