The role of a host star activity and intrinsic magnetic field of a planet with respect to their influence on mass loss of close-in gas giants and definition of the habitable zone for terrestrial exoplanets is discussed. The stellar XUV/EUV radiation and the stellar wind result in ionization, heating, chemical modification, and slow erosion of the upper atmosphere throughout the lifetime of a planet. The closer planet is to the star, the more important is magnetic protection against atmospheric erosion. The consequences of magnetospheric protection of the atmospheres of hot Jupiter’s against stellar winds and the estimation of magnetic moments of such planets via hydrogen (ENA) cloud observations are discussed. We stress that the definition of the HZ for terrestrial exoplanets in the case of low mass M- and K- type stars along with the longer XUV stellar activity periods, should also take into account their relatively close location to the star. This results in importance of the additional “short range” (in astrophysical scales) planetary impacting factors of the stellar activity such as CMEs propagating in the stellar winds. Additionally to that, exoplanets within HZs in close proximity to their host stars may become tidally locked, which, in turn, can result in relatively weak intrinsic planetary magnetic moments. Magnetospheric stand-off distances of weakly magnetized exoplanets at close orbital locations can be shrunk towards the atmosphere, under the action of CMEs. That may have crucial consequences for the loss of planetary atmospheres and their water inventories.