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The observed nuclear X-ray emission in the radio-quiet category of activegalactic nuclei (AGN) is believed to be from a compact region, the coronasituated in the vicinity of the central supermassive black holes (SMBH). Theshape of the X-ray continuum, among other factors, depends on the temperatureof the corona ($\rm{kT_{e}}$). The launch of the Nuclear SpectroscopicTelescope Array (NuSTAR) has led to the determination of the high energycut-off ($\rm{E_{cut}}$; and thereby $\rm{kT_{e}}$) in many AGN. In a handfulof sources, multiple observations with NuSTAR have also revealed changes in$\rm{E_{cut}}$. In this work we aimed to investigate the variation in$\rm{kT_{e}}$ in three AGN, namely NGC 3227, NGC 5548 and MR 2251$-$178 usingmore than one epoch of data on a source from NuSTAR. We carried out spectralanalysis of multiple epochs of data acquired using NuSTAR on the three sourcesincluding a few new observations not published so far. By fittingComptonization model to the data we determined the temperature of the coronaand also investigated changes in $\rm{kT_{e}}$ if any in these sources. In NGC3227, we found evidence for variation in $\rm{kT_{e}}$. We found no correlationof $\rm{kT_{e}}$, photon index ($\Gamma$), reflection fraction ($R$) andoptical depth ($\tau$) with flux, while, $\tau$ is found to anti-correlate with$\rm{kT_{e}}$. These could be due to more than one physical process at work inthe source that causes the change in $\rm{kT_{e}}$. Conclusive evidence for thevariation in $\rm{kT_{e}}$ is not found in MR 2251$-$178 and NGC 5548.

NuSTAR spectral analysis of three Seyfert galaxies: NGC 3227, NGC 5548 and MR 2251$-$178