Narrow-band optical feedback is an effective method of reducing the linewidth and stabilizing the frequency of diode lasers. We have constructed an optically stabilized Al(x)Ga(1-x)As/GaAs laser using a rubidium vapor cell immersed in a dc magnetic field as an optical feedback element. The diode laser's frequency locks to sub-Doppler features of the rubidium spectrum and exhibits a reduction in linewidth from 30 MHz to 35 kHz.