MAP kinase signaling pathways and their roles in the regulation of cytokines and viral replications have not been characterized in influenza-infected pig immune cells. In this study, we found that ERK1/2 and JNK1/2 could both be activated in swine macrophages. We noted that ERK1/2 was phosphorylated and active at a low level constitutively, which may be important for the rapid physiological responses required upon infection.