Incidental learning is a type of informal learning occurring consciously with unintentional acts. Within the scope of this study, informal learning on a digital learning platform was examined in the context of cognitive load. The current study investigated the changes in incidental learning within two different scenarios: extraneous irrelevant content (V1) vs. extraneous relevant content (V2) represented in various modalities. Data were collected in a mixed manner using eye-tracker and electroencephalogram devices. Both incidental and actual learning scores of V2 group were higher than the V1 group. For the incidental learning context, visual modality was superior to other modalities, but the dynamic visuals were perceived as disturbing in comparison to static ones. The V1 group had higher number of errors during task engagement. The eye fixation patterns of both groups were similar to each other. Fixation durations on the dynamic visual extraneous content area were recorded the longest among all extraneous content. The V2 group reported higher mental effort. The efficiency metric calculations yielded contradictory findings depending on the cognitive load values obtained from self-ratings vs. cognitive load index (CLI).