The physical origin of the strong magnetic activity in T Tauri stars and its relation to stellar rotation is not yet well-understood. We investigate the relation between the X-ray activity, rotation, and Rossby number for a sample of young stars in the ~3Myr old cluster IC 348. We use the data of four Chandra observations of IC 348 to derive the X-ray luminosities of the young stars. Basic stellar parameters and rotation rates are collected from the literature. This results in a sample of 82 X-ray detected stars with known rotation periods. We determine the Rossby numbers (i.e. the ratio of rotation period to convective turnover time) of 76 of these stars from stellar structure- and evolution-models for pre-main sequence stars.