Electron-spin-resonance (ESR) spectroscopy was used to study the magnetic structure of the paramagnetic Co58Mn20B10Si12 amorphous alloy, produced by melt spinning. The room-temperature ESR spectrum consisted of two resonance peaks (g=2.00 and g=5.22). The resonance peak at g=5.22 was tentatively attributed to a possible existence of Co2+ ion clusters in the amorphous alloy. It was also shown that the ESR data obtained at different temperatures were consistent with the magnetic measurement, proving that ESR can be a useful tool probing magnetic states in an amorphous metal alloy. Moreover, the ESR spectra from the thermally annealed alloy showed that the peak at g=5.22 is sensitive to the annealing temperature, suggesting that this resonance peak can be used as a signature signal for a magnetic sensor.