Job creep—defined as the gradual and informal expansion of employees' tasks beyond the formal job description without proportionate compensation—has become a hidden challenge in public sector organizations. The present study aims to design a causal-processual model of how this phenomenon unfolds in Iranian public sector organizations, employing a qualitative approach and grounded theory methodology. Data were collected through in-depth semi-structured interviews with 25 employees and managers of the North Khorasan Province Administration and analyzed through the three stages of open, axial, and selective coding. The findings revealed that job creep, as the core phenomenon in this context, is a gradual and compulsory process shaped by the interplay of multi-level causal conditions, including "structural reproduction of manpower shortage", "silent reward system", "episodic administrative shocks", "the unwritten law of absolute obedience", "competence trap", and "economy of favor". These conditions are reinforced by the province's contextual features, such as "resource scarcity", "pact of silence", "error magnification", "local labor market as a lever of pressure", "long arm of the center", and "contentment as passive resistance". In response, stakeholders employ a spectrum of strategies ranging from "competence concealment" and "hidden resistance" to "coalition of no-sayers", "silent transparency", and "cautious negotiation", which are influenced by intervening conditions such as "observant management", "team social capital", and "role boundary keeper". The consequences of this process include "gradual extinction of commitment", "silent brain drain", "organizational breaking point", "symbolic capital erosion", and "administrative epidemic", which in a vicious cycle further intensify job creep. Accordingly, revising job descriptions, establishing a fair compensation system for extra-role duties, empowering employees in role boundary management, and reforming organizational culture are recommended.