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The black hole X-ray binary GX\,339-4 showed an X-ray outburst during 2021.The {\it AstroSat} captured this outburst when the source entered into theintermediate flux state while the count rate was declining. The source showedan alternating flux profile in a timescale of $\lesssim$100 ks, where the hardenergy band was more variable than the soft band. The energy-dependent timingstudy showed that the observed quasi-periodic oscillation (QPO) was prominentin the low energy bands, with its nearly sub-harmonic and harmonic components.These components appear and disappear with time, as observed in the orbit-wiseQPO study. The Q-value, fractional rms, and 4.8-5.6 Hz frequency infer the QPOsas type-B and the spectral state as soft intermediate. The rms spectra of allorbits exhibiting QPOs show an increase in amplitude till $\sim$ 10 keV, beyondwhich it starts decreasing. This may indicate that $\sim$ 10 keV photonscontributed relatively more in QPOs than other energy band photons. TheLorentzian normalization of the type-B QPO in different energy bands isconsistent with the 10 keV peak. The energy-dependent time lag is complex andcould be associated with the Comptonizing corona or jet. Finally, we discusspossible reasons behind the origin of different timing properties observed.

Evolution of low frequency quasi-periodic oscillations in GX 339-4 during its 2021 outburst using AstroSat data