  Variations in the timing of transiting exoplanets provide a powerful tool
detecting additional planets in the system. Thus, the aim of this paper is to
discuss the plausibility of transit timing variations on the Qatar-1 system by
means of primary transit light curves analysis. Furthermore, we provide an
interpretation of the timing variation. We observed Qatar-1 between March 2011
and October 2012 using the 1.2 m OLT telescope in Germany and the 0.6 m PTST
telescope in Spain. We present 26 primary transits of the hot Jupiter Qatar-1b.
In total, our light curves cover a baseline of 18 months. We report on
indications for possible long-term transit timing variations (TTVs). Assuming
that these TTVs are true, we present two different scenarios that could explain
them. Our reported $\sim$ 190 days TTV signal can be reproduced by either a
weak perturber in resonance with Qatar-1b, or by a massive body in the brown
dwarf regime. More observations and radial velocity monitoring are required to
better constrain the perturber's characteristics. We also refine the ephemeris
of Qatar-1b, which we find to be \mbox{$T_0 = 2456157.42204 \pm 0.0001$
\bjdtdb} and \mbox{$P = 1.4200246 \pm 0.0000007$ days}, and improve the system
orbital parameters.
