The variability in partial pressure of carbon dioxide (pCO2) and its control by biological and physical processes in the mixed layer (ML) of the central and eastern Arabian Sea during inter-monsoon, northeast monsoon, and southwest monsoon seasons were studied. The ML varied from 80–120 m during NE monsoon, 60–80 m and 20–30 m during SW- and inter-monsoon seasons, respectively, and the variability resulted from different physical processes. Significant seasonal variability was found in pCO2 levels. During SW monsoon, coastal waters contain two contrasting regimes; (a) pCO2 levels of 520–685 μatm were observed in the SW coast of India, the highest found so far from this region, driven by intense upwelling and (b) low levels of pCO2 (266 μatm) were found associated with monsoonal fresh water influx. It varied in ranges of 416–527 μatm and 375–446 μatm during inter- and NE monsoon, respectively, in coastal waters with higher values occurring in the north. The central Arabian Sea pCO2 levels were 351–433, 379–475 and 385–432 μatm during NE-inter and SW monsoon seasons, respectively. The mixed layer pCO2 relations with temperature, oxygen, chlorophylla and primary production revealed that the former is largely regulated by physical processes during SW- and NE monsoon whereas both physical and biological processes are important in inter-monsoon. Application of Louanchiet al (1996) model revealed that the mixing effect is the dominant during monsoons, however, the biological effect is equally significant during SW monsoon whereas thermodynamics and fluxes influence during inter-monsoons.