We demonstrate that the submonoid membership problem and the rational subset membership problem are equivalent in Artin groups. Both these problem are undecidable in a given Artin group if and only if the group embeds the right-angled Artin groups of rank 4 over a path or a square; and this can be characterized using only the defining graph of the Artin group. These results generalize the ones by Lohrey - Steinberg for right-angled Artin groups. Moreover, both these decision problems are decidable for a given Artin group if and only if the group is subgroup separable. This equivalence for right-angled Artin groups is provided by Lohrey - Steinberg and Metaftsis - Raptis. The equivalence for general Artin groups comes from some observations here and the characterization of separable Artin groups by Almeida - Lima.