The angular force model of Clark, Gazis and Wallis (CGW) have been applied to calculate the phonon frequencies of antiferromagnetic Fe-30%Mn alloy. Furthermore, the second order elastic constants of the alloy have been computed using a new empirical many body potential (MBP), which has been developed by Akgun and Ugur. The parameters defining the MBP for the alloy have been computed following a procedure given by Akgun and Ugur. The computed elastic constants have been used to calculate the phonon frequencies of the alloy. Finally the theoretical results have been compared with the corresponding experimental values.