  The aim of this work is to identify and study the stellar objects with
variable EW(Ha) in the young stellar cluster IC 348. We performed photometric
and slit-less observations at several epochs in order to reveal the variable
objects. Significant variability of EW(Ha) was found in 90 out of 127 examined
stars. From all epochs of observations, 32 objects were classified as CTT and
69 as WTT objects. The fraction of the variables in these samples is about 60%.
We also identified 20 stellar objects, which showed not only a significant
variability of the equivalent width, but which also change their apparent
evolutionary stage.
  The analysis of data obtained over a wide wavelength range (from X-ray to
mid-infrared) has shown that Ha activity and the measure of its variability are
in good agreement with the activity of stellar objects measured with its other
parameters, such as X-ray radiation and the mass accretion rate. The EW(Ha)
differs not only between objects at different evolutionary stages, but also
between variable and non-variable objects. The variables in the CTT and WTT
samples are more active than non-variables although they have almost the same
evolutionary age. Another distinct difference between these variables and
non-variables is their average masses. The variables from both CTT and WTT
samples are noticeably more massive than non-variables. Our data confirm the
assumption made for other star formation regions, that the decay of accretion
activity occurs more slowly for more massive CTT objects. Apparently, a similar
trend is also present in WTT objects, which are at a later stage of evolution.
The variability of the stellar objects, which change their evolutionary
classes, at least in a fraction of them, is due to the fact that they are close
binaries, which affects and modulates their Ha emission activity.
