Combustion reactions were observed during the room temperature ball milling of some metal powders (Zr, Ti, and Fe) in oxygen gas. A sharp increase in the temperature of the milling container during milling was monitored. X-ray diffraction analysis of the samples after milling reveals the formation of metal oxides, suggesting the occurrence of oxidation reactions induced by ball milling treatment. It is also found that higher milling intensities, using heavier balls, more balls and magnets, causes shorter ignition times.