The corrosion of metallic biomaterials under physiological conditions remains a critical challenge due to the risk of ion release affecting biocompatibility. In this study, the time-dependent electrochemical behavior of a poly(vinyl alcohol) (PVA)/chitosan biopolymer coating applied to biomedical-grade steel was evaluated to assess its protective performance. The coating was prepared via dip-coating using a 9.9:0.1 PVA/chitosan formulation and characterized by FTIR and Raman spectroscopy to confirm intermolecular interactions and film formation. Electrochemical impedance spectroscopy was employed over 216 h of immersion in Hanks’ Balanced Salt Solution to monitor coating degradation and corrosion mechanisms. The coated system exhibited a significant increase in the low-frequency impedance modulus from approximately 1200–1400 to 5000–6000 Ω·cm², indicating enhanced barrier properties and interfacial stability compared to uncoated steel. Equivalent circuit analysis revealed a transition from a predominantly capacitive, barrier-controlled response at early immersion stages to diffusion-influenced behavior at longer exposure times, associated with electrolyte penetration and interfacial processes. Overall, the PVA/chitosan coating effectively delays corrosion reactions and maintains high impedance under simulated physiological conditions, demonstrating its potential as a protective and biocompatible surface modification for metallic biomedical applications.