This study, based on an online instruction via the web conferencing system, explores extraneous cognitive load and its influence on the learning process. Sixty-two sophomore students who enrolled in an online introductory programming course participated in the study. An observation form was used to analyse the course records in video format. Interviews with selected participants were conducted in order to clarify the students' behaviours during the instructional process. The results indicated that the extraneous cognitive load elements (coherence, redundancy, modality, signalling, and temporal-spatial contiguity) influenced the instructional process. The results suggested that, in web conferencing systems extraneous cognitive load appeared not only from design features of multimedia materials but also the delivery settings. Future work is needed to put forward the influences of the load elements caused in various platforms. The implications and suggestions for instructors who plan to design and teach online courses via web conferencing were also provided.