The processing of extramusical meaning can be reflected in N400 effects of the ERP. However, how conceptual representations can be activated in music still needs to be specified. We investigated the activation of iconic meaningful representations in music by using a cross‐modal semantic priming paradigm with an implicit task. Pictures of spatial scenes were semantically congruent or incongruent to preceding music in three stimulus onset asynchrony (SOA) conditions. The results revealed that the semantically incongruent target pictures elicited larger N400 amplitude than the congruent target pictures. Moreover, the semantic priming effect was modulated by the SOAs. The N400 effect was observed in the 200‐ms and 800‐ms SOA conditions, but not in the 1,200‐ms SOA condition. These results suggest that extramusical meaning purely due to iconic sign quality can be activated, and that the conceptual activation in music can be rapid and automatic.