Complex AC susceptibility was measured systematically as a function of temperature at different AC field amplitudes H A C and frequencies f for a melt-grown YBa 2 Cu 3 O 7 - δ , sample. Based on the flux creep model of Feigel'man et al., the dependence of the peak temperature T p in χ'' on and H A C can be well explained and the important parameter t 0 of 10 - 5 s (f 0 = 1/t 0 = 10 5 Hz) was extracted. Because we have measured flux creep over the times t(= 1/f) 10 - 6 s =< t =< 10 - 2 s, the condition t t 0 to was proved to be invalid for some of the measurement frequencies higher than f 0 . Therefore, we have detected the creep at times t ~ t 0 (f ~ f 0 ).