Activity in the SPB star 53 Piscium

New spectroscopic observations of the star 53 Psc are presented. A correlation technique has been used to derive the radial velocity curves with a high accuracy. Four frequencies have been detected in the radial velocity variations using four frequency analysis algorithms. Three frequencies (1.81, 1.22 and 1.57 cd(-1)) are typical SPB star frequencies, the last one being close to our detection threshold. They are associated to low amplitude velocities, of the order of 1-2 km s(-1). So we classify 53 Psc in the SPBs class in agreement with its position in the HR diagram. Line equivalent width and central depth variations are also observed. Two phenomena appear: first, a smooth variation, present in all lines with a time scale of 10 days, could be related to the stellar rotation and a magnetic field. Second, on two consecutive nights, a sudden and important increase (20%) of equivalent widths and central depths of H delta and He I lines could be due to an outburst similar to the ones present in some Be stars. The variation in the equivalent widths is mainly due to the increase of the central depth of the quoted lines. This suggests the existence of NLTE effects due to a hot low density plasma in the upper layers of the atmosphere of 53 Psc. An additional frequency is pointed out around 0.11 cd(-1). The best interpretation is an SPB frequency shifted by rotation.