Biological agents have had a tremendous effect in the management of rheumatoid arthritis (RA). However, subsequent infection is regarded as an emerging problem owing to the suppression of host immunity by these agents. Cellular immunity with T lymphocytes plays a crucial role in host defense against mycobacterial infections; hence, immunosuppression due to these biological agents may lead to tuberculosis (TB) and nontuberculous mycobacteria (NTM) infections. Therefore, pretreatment screening for TB and NTM infection and appropriate management are crucial. In general, the lungs are the major site of infection caused by mycobacteria, and the disease may typically have a chronic course. Thus, persistent respiratory symptoms and signs trigger suspicion of pulmonary TB or NTM infection, and chest radiography as well as sputum examination plays a major role in the diagnosis. In addition, promising diagnostic tools such as interferon-gamma release assay (IGRA), anti-MAC antibody measurement, and Xpert MTB/rifampin (RIF) assay are newly available. Further research is needed to verify these assays. As a rule, to avoid development of drug-resistant strains, treatment with multiple drugs for a relatively extensive duration is required for therapy.