Analysis of VLBI records of distant radio source signals allows to determine the proper motions of the extragalactic objects with an accuracy of a hundred microseconds of arc per year (muas/yr). Such an accuracy is sufficient to investigate the aberration in proper motions of distant bodies due to the rotation of the Solar system barycentre around the Galactic centre. We analyzed geodetic and astrometric VLBI data to produce radio source coordinate time series using the CALC/SOLVE software package. We fitted vector spherical harmonic components of degree 1 and 2 to the velocity field made up of the proper motions of 555 sources of good observational history over the period 1990-2010. The acceleration vector has an amplitude of 6.4 /-1.5 muas/yr and is directed towards equatorial coordinates alpha=263° and delta=-20°. Within errors bars, the magnitude and the direction of the dipole component agree with predictions (magnitude 4-6 muas/yr, alpha=266° and delta=-29°).