Recent research has introduced some evidences referring to a possible connection between the variation in geomagnetic field measurements and seismic activities. Thus, the present study focuses on a certain seismic activity that occurred at the northern part of Honshu Island, Japan to find out its impact on the diurnal geomagnetic variations recorded at this region. The study of variability of daily geomagnetic variations amplitude at the northern part of Honshu Island; which is characterized by high seismic activities has introduced motivating results. Data analysis and processing indicate the presence of an unusual change in the diurnal variations amplitude in association with earthquake activity occurred on 24 March 2008 at the studied area. A remarkable anomalous behavior in the diurnal variations amplitude of the East-West horizontal geomagnetic component (D-component) was detected in the vicinity of the epicenter at the Tohno station compared with those recorded at the Kakioka geomagnetic observatory and other remote reference stations. This anomalous behavior is observed only during the day of the studied seismic event, which suggests a possible connection between the earthquake occurrence and the change of diurnal variations range. Moreover, since there were no significant external geomagnetic changes during the occurrence of earthquake as revealed from the Dst and Kp indices, the observed anomalous variability in the diurnal geomagnetic variations range of D-component can be considered as anomalous phenomenon linked with the studied seismic activity. Such anomalous phenomenon can be used for constructing earthquake warning systems.