This paper describes the noise spectra of tunneling magnetoresistive (TMR) heads as a function of both the dc bias current and the external magnetic field in order to understand the influence of resistance area (RA) product on the noise in the TMR head. The strong noise spectral peak appears in the frequency range between 4.0 and 7.0 GHz, which is ascribed to the thermally excited magnetization fluctuation noise (thermal mag-noise) originated from the free layer. This peak intensity, linewidth, and noise power strongly depend on both the dc bias current and the external magnetic field. These features mean that the peak is strongly influenced by the spin torque (ST) with increasing dc bias current in case that the magnetization of the free and reference layers is nearly antiparallel to each other. In addition, this noise power markedly strengthens with the RA and the size reductions in the TMR head. On the basis of this result, it is pointed out that the influence of the ST on the thermal mag-noise is markedly enhanced since the dc bias current density increases with both the RA and size reductions in the TMR head.