  Quasi-periodic oscillations (QPOs) have been detected in many Fermi-detected
bright blazars. In this letter, we report multiple QPOs detected in a
non-blazar AGN PKS 0521-36 searched over the entire 15 years of Fermi-LAT data.
QPOs are detected at 268 days, at 295 days, and at 806 days timescales with
more than 3$\sigma$ significance. The QPO detected at 806 days happens to be
the third harmonic of QPO at 268 days. The time scales are consistent in both
Lomb-Scargle and Wavelet analysis. Furthermore, the Gaussian Process modeling
of the light curve is performed with stochastically driven damped harmonic
oscillator (SHO) and damped random walk (DRW) modeling to uncover the presence
of QPOs. The constructed power spectral density (PSD) exhibits two QPOs, with
observed timescales of approximately 283 days and 886 days. This is the first
non-blazar AGN where the long-term QPO is detected. Earlier studies show this
source has a weak beamed jet. The exact cause for these QPOs remains unclear.
We also assembled the $\gamma$-ray QPO detected in various blazar and tested
the QPO time scale dependent on the black hole mass. No significant correlation
is found.
