The high temperature oxidation at 850 °C of a lab-rolled low-density steel grade, containing 4.85 wt.% Mn, 4.75 wt.% Al was investigated experimentally and by means of numerical simulations. Experimental results showed clear signs of oxidation, both externally as well as internally even at short oxidation times of 5 minutes during heat treatments. The external oxides were mostly comprised of iron and manganese-rich oxides, whilst the internal oxides contained mostly aluminium and manganese-rich oxide phases. Numerical simulations for internal oxidation conditions could confirm the formation of oxides, predominantly along the grain boundaries. However, computed oxidation depths are much smaller than experimental values, which may be due to the fact that the geometric hinderance of formed oxide phases was over-emphasised in the numerical simulations. Nevertheless, the obtained results agree qualitatively with the trends, observed in the experiments and spark further need to additional studies.