  The Multi-site All-Sky CAmeRA (MASCARA) aims to find the brightest transiting
planet systems by monitoring the full sky at magnitudes $4<V<8.4$, taking data
every 6.4 seconds. The northern station has been operational on La Palma since
February 2015. These data can also be used for other scientific purposes, such
as the study of variable stars. In this paper we aim to assess the value of
MASCARA data for studying variable stars by determining to what extent known
variable stars can be recovered and characterised, and how well new, unknown
variables can be discovered. We used the first 14 months of MASCARA data,
consisting of the light curves of 53 401 stars with up to one million flux
points per object. All stars were cross-matched with the VSX catalogue to
identify known variables. The MASCARA light curves were searched for periodic
flux variability using generalised Lomb-Scargle periodograms. If significant
variability of a known variable was detected, the found period and amplitude
were compared with those listed in the VSX database. If no previous record of
variability was found, the data were phase folded to attempt a classification.
Of the 1919 known variable stars in the MASCARA sample with periods $0.1<P<10$
days, amplitudes $>2\%$, and that have more than 80 hours of data, $93.5\%$ are
recovered. In addition, the periods of $210$ stars without a previous VSX
record were determined, and $282$ candidate variable stars were newly
identified. The O'Connell effect is seen in seven eclipsing binaries, of which
two have no previous record of this effect. MASCARA data are very well suited
to study known variable stars. They also serve as a powerful means to find new
variables among the brightest stars in the sky. Follow-up is required to ensure
that the observed variability does not originate from faint background objects.
