Deep J,H, and K ^ { \prime } images obtained with the Canada-France-Hawaii Telescope adaptive optics system are used to investigate the metallicity of red giant branch ( RGB ) stars in three fields in the disk of the Local Group dwarf irregular galaxy NGC 6822 .
The slope of the RGB on the ( K,J - K ) 
color-magnitude diagrams indicates that \overline { [ Fe / H ] } = -1.0 \pm 0.3 .
The locus of the RGB is bluer than that of globular clusters with the same RGB slope , by an amount that is consistent with the majority of RGB stars in these fields having an age near 3 Gyr .
It is demonstrated that if RGB stars in NGC 6822 are this young then the metallicity computed from the RGB slope may be \sim 0.05 dex too low .
Finally , the metallicity computed from the RGB slope is lower than spectroscopic-based metallicities for young stars in NGC 6822 , and it is concluded that \frac { \Delta [ Fe / H ] } { \Delta t } = -0.2 \pm 0.1 dex Gyr ^ { -1 } in NGC 6822 during the past few Gyr .