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We analyze the 11-year long-term light curve of the Radio-loud Narrow-lineSeyfert 1 (NLSy1) galaxy J0849+5108 and the nearly simultaneous $\gamma$-raydata of the source. The data were obtained with the Owens Valley RadioObservatory 40-m telescope at 15~GHz and with the Large Area Telescope onboardFermi Gamma-ray Space Telescope, respectively. A quasi-periodic oscillation(QPO) signal at a significance of $>$5$\sigma$ is found in the radio lightcurve, but no similar modulation is seen in the $\gamma$-ray light curve. TheQPO signal was present for 21 cycles, the longest among the reported radioQPOs, and likely disappeared after 2019 January 16. Different mechanismsproposed to explain the observed QPOs in Active Galactic Nuclei (AGN) arediscussed for this QPO case. Either a secular instability in the inneraccretion disk or a helical structure in the jet of J0849+5108 may explain theradio QPO, while for the latter scenario the jet has to be collimated up to$\sim$200~pc, similar to that seen in the nearby AGN M87. It will be ofinterests to keep monitoring the source at radio frequencies, seeing if similarQPO signals would appear again or not.

A Radio Quasi-periodic Oscillation of 176 day in the Radio-loud Narrow-line Seyfert 1 Galaxy J0849+5108