Aim: The aim of this study is to examine the legal regulation of law enforcement and national security applications within the framework of the European Union’s Artificial Intelligence Regulation, the AI Act. The study seeks to determine what changes the AI Act will bring to the legal environment of covert investigations and how it should be applied to law enforcement and national security agencies. Methodology: The research employs legal analysis, comparative legal study, and literature review. The study compares the definitions of the AI Act and the OECD, as well as national legislation, to provide a comprehensive view of the legal definition and application of AI systems in the fields of law enforcement and national security. Findings: The AI Act adopts a technology-neutral approach to the definition of artificial intelligence systems to keep pace with rapid technological and market developments. The study finds that the legal definitions of autonomy, adaptability, and inference capability will pose significant challenges for legal practitioners. Additionally, it establishes clear rules for law enforcement agencies, while the AI Act is not applicable to national security applications. The study highlights the role of the National Security Service (NBSZ) as a central technology provider for both law enforcement and national security agencies. The NBSZ must ensure that its services comply with the requirements of the AI Act when providing them for law enforcement purposes. Value: The article contributes to the understanding of the legal regulation of artificial intelligence systems, particularly concerning their application in law enforcement and national security. The study clarifies that different regulatory frameworks apply to the legal compliance of AI technology in law enforcement and national security contexts. It emphasizes the role of the NBSZ, which is crucial in ensuring technological and legal compliance in the application of AI systems for law enforcement purposes.