  We report on the detection of extended $\gamma$-ray emission from lobes in
the radio galaxy NGC 6251 using observation data of Fermi Large Area Telescope
(Fermi-LAT). The maximum likelihood analysis results show that a radio
morphology template provides a better fit than a point-like source description
for the observational data at a confidence level of 8.1$\sigma$, and the
contribution of lobes accounts for more than 50\% of the total $\gamma$-ray
flux. Furthermore, the $\gamma$-ray energy spectra show a significant disparity
in shape between the core and lobe regions, with a curved log-parabola shape
observed in core region and a power-law form observed in lobes. Neither the
core region nor the northwest lobe displays the significant flux variations in
the long-term $\gamma$-ray light curves. The broadband spectral energy
distributions of both core region and northwest lobe can be will explained with
a single-zone leptonic model. The $\gamma$-rays of core region are due to the
synchrotron-self-Compton process while the $\gamma$-rays from northwest lobe
are interpreted as inverse Compton emission of the cosmic microwave background.
