I am currently working on an alien planet which is inhabited by a race that looks "somewhat" humanoid. My question is, just because they have a similar strusture with humans, would they have a similar anatomy? (Respiratory system, digestive sytem, heart, brain etc.)
This is a tough one. There is such a thing as convergent evolution - two creatures evolving to have similar attributes despite being unrelated. Think, dolphins - which evolved from deer - and sharks. Both evolved in the ocean. So if an alien evolved under similar circumstances, it could happen. First, you would need a vertebrate-type creature somewhere in the tree of life. Then you would need one with ganglia, then it would naturally evolve a cranium from there I think - some kind of casing to protect it. From there, sensory organs like eyes and ears would probably naturally evolve around the ganglia. Then the creature would need a way to breathe outside of water - but there's no reason it has to be in that order. They could already be breathing on land before they evolve ganglia. One thing is for sure - life would definitely have had to evolve in a substrate like water before it transitioned to land. Anyway, humans then evolved from tree climbing rodents that turned into tree-dwelling primates, and so on and so forth. So probably the alien species would evolve under similar circumstances, but their anatomy would probably come up with their own solutions to problems, such as breathing. Perhaps instead of lungs, they could continue to breathe through their skin - of course, that would come with its own challenges. This is all assuming they even need to respirate tho.
Anyway, in sum - similar environmental pressures, different anatomical solutions, will get you there.