It is crucial to control NOx emission into the atmosphere because it can make several harmful health and environmental effects. Many techniques are available for NOx reduction, and among them, selective catalytic reduction (SCR) is one of the most efficient techniques for NOx removal in flue gas cleaning process. The reduction of NOx by CO offers a simple and low-cost technology for reducing NOx emissions from mobile or stationary sources. In this review, NOx emission, different NOx control technologies, and the challenges for the SCR process are studied. This paper reviews various types of catalysts, including supported and unsupported metal oxide catalysts as efficient catalysts for NOx reduction by CO. The reported experimental researches are analyzed to make an overview of the NOx reduction through CO-SCR process. Moreover, catalytic performances in the presence of oxygen, water steam, and sulfur dioxide, which usually exist in exhaust gases produced in the combustion process, are discussed. Moreover, this paper reviews the possible reaction mechanisms for the CO-SCR.