We report the results of calculations of pseudoscalar-isoscalar hadronic current correlators using the Nambu--Jona-Lasinio model and the real-time finite-temperature formalism. Results are presented for the temperatures range 1.2 $\leq T/T_c\leq$ 6.0, where $T_c$ is the temperature of the confinement-deconfinement transition, which we take to be $T_c=170$ MeV. Two important resonant features are seen in our calculations. In order to understand the origin of these resonances, we have performed relativistic random phase approximation (RPA)calculations of the temperature-dependent spectrum of the $η$ mesons for $T

20 pages, 10 figures, Revtex4