  We present a study of metallicities in a sample of main sequence stars with
spectral types M, K, G and F ($T_{\rm eff}$ $\sim$ 3200 -- 6500K and log $g$
$\sim$ 4.3 -- 5.0 dex) belonging to the solar neighborhood young open cluster
Coma Berenices. Metallicities were determined using the high-resolution
(R=$\lambda$/$\Delta$ $\lambda$ $\sim$ 22,500) NIR spectra ($\lambda$1.51 --
$\lambda$1.69 $\mu$m) of the SDSS-IV APOGEE survey. Membership to the cluster
was confirmed using previous studies in the literature along with APOGEE radial
velocities and Gaia DR2. An LTE analysis using plane-parallel MARCS model
atmospheres and the APOGEE DR16 line list was adopted to compute synthetic
spectra and derive atmospheric parameters ($T_{\rm eff}$ and log $g$) for the M
dwarfs and metallicities for the sample. The derived metallicities are near
solar and are homogeneous at the level of the expected uncertainties, in
particular when considering stars from a given stellar class. The mean
metallicity computed for the sample of G, K, and M dwarfs is
$\langle$[Fe/H]$\rangle$ = +0.04 $\pm$ 0.02 dex; however, the metallicities of
the F-type stars are slightly lower, by about 0.04 dex, when compared to cooler
and less massive members. Models of atomic diffusion can explain this modest
abundance dip for the F dwarfs, indicating that atomic diffusion operates in
Coma Berenices stars. The [Fe/H] dip occurs in nearly the same effective
temperature range as that found in previous analyses of the lithium and
beryllium abundances in Coma Berenices.
