We report the first extensive observations of the binary dMe flare star AT Mic made simultaneously at optical, infrared and microwave wavelengths. The observations have failed to show decreases in infrared flux at the time of optical flares. Such decreases are expected if the inverse Compton scattering mechanism proposed by Gurzadyan is dominant during the flares. On the contrary, one large flare showed a significant increase in the K-band flux consistent with an energy spectrum which is flat, at least in the range from U to K bands. The J-band flux, however, showed no significant average change during a large number of smaller flares. These results are discussed in terms of a number of thermal and non-thermal flare models. It is concluded that the data can be best accounted for in terms of a hot (∼105 K) plasma flare model which produces a relatively flat energy-spectrum over a range of wavelengths determined by the temperature, density and depth of the source region. This range may therefore vary from flare to flare and from star to star. Microwave observations during a large number of optical flares indicate a variation of at least several orders of magnitude in the ratio of optical to microwave flare luminosities. This is taken to imply that different plasmas are responsible for the two emissions.