Optineurin has been shown to be involved in primary open-angle glaucoma. We recently found that optineurin is involved in familial amyotrophic lateral sclerosis (ALS). On the other hand, optineurin has been shown to inhibit transcription factors related to innate immunity such as NF-kappa B and interferon regulatory factor-3 (IRF3). In the present study, the effect of ALS-associated optineurin mutations on IRF3 activation was investigated. Optineurin inhibited IRF3 activation induced by melanoma differentiation-associated gene 5 or Toll-IL-1 receptor domain-containing adaptor-inducing interferon-beta. The inhibition was abrogated by mutations related to ALS but not by a mutation related to glaucoma. Reporter assay indicated that the JAK-STAT signaling pathway was not affected by optineurin. These results show that ALS-related optineurin is involved in the IRF3 activation pathway. Pathogenesis of ALS may be associated with some kind of innate immunity, especially that against virus infection, through IRF3 activation.