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We present here the detection of a possible quasi-periodic oscillation (QPO) signal in the X-ray light curve of the active galactic nucleus 3C 120, a broad line radio galaxy at <i>z</i> = 0.033. The hint of a QPO at the 3<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>σ</mi></semantics></math></inline-formula> level at 7.1 × 10<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mrow><mo>−</mo><mn>6</mn></mrow></msup></semantics></math></inline-formula> Hz (∼1.65 days) was detected based on the analysis of X-ray data acquired in the 3–79 keV band by the <i>Nuclear Spectroscopic Telescope Array (NuSTAR)</i>. The data, when processed separately in the soft (3–10 keV), hard (10–79 keV) and the total (3–79 keV) bands using four different techniques, namely discrete correlation function, Lomb Scargle periodogram, structure–function, and power spectral density indicated the presence of a QPO. 3C 120 very well fits in the negative correlation in the frequency of the QPO versus the black hole mass (F<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mrow><mi>Q</mi><mi>P</mi><mi>O</mi></mrow></msub></semantics></math></inline-formula> versus M<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mrow><mi>B</mi><mi>H</mi></mrow></msub></semantics></math></inline-formula>) diagram known for stellar-mass and supermassive black hole sources. Considering the observed signs of QPO to represent the innermost stable orbit of the accretion disk, we found a black hole mass of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>1.9</mn><mo>×</mo><msup><mn>10</mn><mn>9</mn></msup></mrow></semantics></math></inline-formula> M<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mo>⊙</mo></msub></semantics></math></inline-formula> for a Kerr black hole and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>3.04</mn><mo>×</mo><msup><mn>10</mn><mn>8</mn></msup></mrow></semantics></math></inline-formula> M<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mrow></mrow><mo>⊙</mo></msub></semantics></math></inline-formula> for a Schwarzschild black hole. This deduced black hole mass from QPO measurement is a few times larger than the black hole mass obtained from reverberation mapping observations.