Usable Artificial Intelligence (AI) application refers to an AI solution that is characterized by the easiness of use and learning through an optimum interface established by a proficient Human-Computer Interface (HCI) design. This article reviews the related literature to find out the importance of HCI to make AI valuable and usable. The article also investigates the possible solutions and guidelines that ensure the usability of AI-powered applications as well as the corresponding challenges of designing usable AI. It also essentially explores several usability evaluation methods employed by recent studies. The findings demonstrate the substantial role of HCI in designing Human-centred AI (HAI) applications. HAI lets AI applications support humans instead of replacing them and grants user's better control over security and privacy. No standard usability measures exist and more research is required especially on the issues of interpretability, integrability, and collaboration.