The Mbssbauer spectrum of amorphous alloys in radio frequency field shows a collapse effect. By means of the measurement of the thermal red shift of the spectrum and the observation of the aftereffect of a relatively stronger rf field the mechanism of the collapse effect was investigated. The temperature increases of the samples showing a full collapse effect in a rf field were calculated. It is concluded that samples in rf field remain below the Curie temperature. The aftereffect can be well understood with the model based on the random fluctuation of magnetic atomic clusters caused by rf field. It is confirmed that the collapse effect observed is exerted by the rf induced random fluctuation of magnetic clusters rather than a ferromagnetic- paramagnetic transition in consequence of the rf heating.