it depends on the precise definition to some degree, because positivism has become a term which has seen very wide use for a whole range of things which have only the common relation of being related to science having some special claim to truth, as opposed to philosophy. in terms of the philosophy of positivism, however, marxism is opposed to it.
lenin’s materialism and empirio-criticism, and in particular althusser’s discussion of it are good for showing the wide gap between marxism and positivism. the empirio-critics were essentially subjective idealists who believed reality was made up only of sense-impressions, and that the advances of science had proved that matter has “disappeared”. lenin’s argument against that is essentially one which sees matter as a category, the form of matter remains intact to a large degree, even as the content changes to express further advances in our knowledge of how matter manifests itself. a positivist on the other hand, at least in the old-fashioned sense, would dismiss this as a metaphysical claim and thus not verifiable (the same basis on which ayer, for example, said he wasn’t an atheist because the question of god’s existence at all is one which is “nonsensical” in that it makes claims that go beyond empirical experience)