The magnetic properties of Fe-Mn-Al alloys in the disordered phase are investigated through the M\"ossbauer technique. The magnetic phase diagram in the bcc structural phase is obtained as a function of the Al concentration ($q$) and Mn concentration ($x$). The site-diluted Ising model proposed in a previous study of the Fe-Al system is extended to the present ternary alloy. Rather good fits of the experimental phase diagram, as well as the mean hyperfine field as a function of concentrations $q$ and $x$, are obtained by using the same fitted values for the parameters of the exchange interaction $J(q)$ of the Fe-Al binary system.