A simple site-diluted Ising model is proposed to study the magnetic properties of ${\mathrm{Fe}}_{p}{\mathrm{Al}}_{q}$ alloys (with $p+q=1)$ in the structural disordered phase. It is assumed that Al atoms, which are nonmagnetic, can induce an extra ferromagnetic interaction between second-neighbor Fe atoms. It is further assumed that this second-neighbor interaction, as well as the nearest-neighbor one, decreases as q increases. The critical properties are obtained by the variational approach based on Bogoliubov inequality for the free energy in the pair approximation. Quite good fittings to the experimental results of the ordering temperature are obtained as a function of q. A negative value of the extra exchange interaction for some range of the Al concentration is obtained. It is argued that this negative exchange can drive a spin-glass-like phase in these compounds, a fact that should be sought experimentally.