An optical magnetometer capable of measuring static as well as dynamic magnetic fields is presented. An all-fiber Mach-Zehnder interferometer powered by a laser diode was used to measure the strain of a metallic glass strip. Using a magnetic feedback technique and an ac magnetic bias field, a minimum detectable field of 5 Gauss in a 1 Hz equivalent noise bandwidth was achieved. The magnetometer responds linearly from 0 Hz to a 3 dB bandwidth of 253 Hz and has a dynamic range of more than 100 dB.