  We study the effect of an imposed magnetic field on the motion of charged
dust particles in magnetically active regions of a protoplanetary disc.
Assuming a power law structure for the vertical and the toroidal components of
the magnetic field for the regions beyond magnetically dead region of the disc,
the radial and the vertical velocities of the charged particles, in the
asymptotic case of small particles, are calculated analytically. While grains
with radii smaller than a critical radius significantly are affected by the
magnetic force, motion of the particles with larger radii is independent of the
magnetic field. The critical radius depends on the magnetic geometry and the
charge of the grains. Assuming that a grain particle has one elementary charge
and the physical properties of the disc correspond to a minimum-mass solar
nebula, we show that only micron-sized grains are affected by the magnetic
force. Also, charge polarity determines direction of the radial velocity. For
such small particles, both the radial and the vertical velocities increase due
to the magnetic force.
