  The relative cosmic variance ($\sigma_v$) is a fundamental source of
uncertainty in pencil-beam surveys and, as a particular case of count-in-cell
statistics, can be used to estimate the bias between galaxies and their
underlying dark-matter distribution. Our goal is to test the significance of
the clustering information encoded in the $\sigma_v$ measured in the ALHAMBRA
survey. We measure the cosmic variance of several galaxy populations selected
with $B-$band luminosity at $0.35 \leq z < 1.05$ as the intrinsic dispersion in
the number density distribution derived from the 48 ALHAMBRA subfields. We
compare the observational $\sigma_v$ with the cosmic variance of the dark
matter expected from the theory, $\sigma_{v,{\rm dm}}$. This provides an
estimation of the galaxy bias $b$. The galaxy bias from the cosmic variance is
in excellent agreement with the bias estimated by two-point correlation
function analysis in ALHAMBRA. This holds for different redshift bins, for red
and blue subsamples, and for several $B-$band luminosity selections. We find
that $b$ increases with the $B-$band luminosity and the redshift, as expected
from previous work. Moreover, red galaxies have a larger bias than blue
galaxies, with a relative bias of $b_{\rm rel} = 1.4 \pm 0.2$. Our results
demonstrate that the cosmic variance measured in ALHAMBRA is due to the
clustering of galaxies and can be used to characterise the $\sigma_v$ affecting
pencil-beam surveys. In addition, it can also be used to estimate the galaxy
bias $b$ from a method independent of correlation functions.
