This study is a first attempt at formalizing the concept of Musical Relevance from a cognitive and computational perspective. We elaborate on Sperber and Wilson's Relevance Theory, and extend it to account for musical cognition, involving both listening and understanding. Our claim is that the application of the concept of Cognitive Relevance to music would permit us to partially explain hearers' behavior and composers' choices. A computational model of Musical Relevance could also contribute to the formulation of a general computational theory of musical cognition. In turn, formulating an algorithm to compute Musical Relevance can shed light on the computational nature of the broader cognitive principle of relevance. We propose to unify Relevance Theory with the Generative Theory of Tonal Music, in order to compute Musical Relevance. We started implementing a system to test the proposed approach over simple examples and report about the results in a preliminary experimentation.