The magnetic field and temperature dependence of the low frequency magnetic response of antiferromagnetically coupled Fe/Cr(100) multilayers has been studied between +/-500 Oe , from 2 to 300 K . At T = 2 K the losses exhibit an unusually strong frequency dependence which can be described within a single relaxation time scheme. This relaxation time proves to be strongly field dependent. These phenomena are specific for epitaxial multilayers with large magnetoresistance. The behavior of the relaxation time at low temperatures might be related to some quantum tunneling processes.