Uninterrupted and affordable access to electricity in the national territory is essential for the realization of daily life activities. National Energy Security can be understood as the capacity of the State to guarantee sufficient uninterrupted energy availability in a sustainable and affordable manner for the entire population. Mexican electricity set of policies related to national energy security have been crucial as part of the national political and economic policies implemented in modern times. The purpose of this article is to analyze the impact of the Mexican national electricity related to National Electric Security through the estimation of a National Energy Security Index (NESI) over a 50-year period, from 1970 to 2020. As part of the estimation procedure, it is possible to assess four dimensions related to this energy source: Availability (AV), Applicability (AP), Acceptability (AC), and Affordability (AF). The results suggest that while the National Energy Security Index (NESI) showed a moderate increased overtime, differences arising when analyzing each dimension separately. Particularly, the affordability aspect (AF) has a positive and sustained relevance at the national level, regardless of the prevailing national economic model or administration. Conversely, the availability (AV) dimension showed downward trend along the period of study, pattern associated to the dependence of oilfield discoveries and the lack of investment in exploration, extraction, and refining of hydrocarbons and the consequent steady increase in imports. We believe these results contribute in that they shed new light on the scope of Mexican electricity policy throughout the period analyzed and provide useful input for the prospective design of policies in the electricity sector.