We study the minimality of some natural matrix groups defined on nice topological fields F. More precisely, we examine the minimality of the special upper triangular groups SUT(n, F), the special linear groups SL(n, F) and the projective general linear groups PGL(n, F). We prove that if F is a local field of characteristic different than 2, then SUT(n, F) is minimal for every n ∈ N. This result is new even for F = R and n = 2. In contrast, we show that SUT(3, Q(i)) is not minimal, where Q(i) is the Gaussian rational field.Using Iwasawa decomposition our technique leads to the total minimality of SL(n, F) for local fields F of characteristic different than 2. Note that recent results of Bader and Gelander [2], obtained in a different way, imply that the same is true for every characteristic. This extends the well known result of Remus and Stoyanov [19] about the total minimality of SL(n, R).Moreover, we show that if F is a local field, then PGL(n, F) is totally minimal for every n ∈ N.