The 1/f resistance fluctuations of carbon fiber are observed under four different nonequilibrium conditions controlled by the heat diffusion from the fiber to the external environment. A higher-order correlation function of an observed 1/f time series is analyzed and compared with those of three different types of computer-generated 1/f time series. It is found that the higher-order correlation function related to the time-inversion asymmetry of the 1/f resistance fluctuation shows the same statistical property as that of a one-dimensional diffusion system. Further more, the higher-order correlation function of the 1/f resistance fluctuations with the same 1/f spectra is shown to be affected by the heat diffusion from the carbon fiber.