Dioxygenase that specifically demethylates N(6)- methyladenosine (m6A) RNA, the most prevalent internal modification of messenger RNA (mRNA) in higher eukaryotes (PubMed:23177736, PubMed:24489119, PubMed:24616105, PubMed:24778178, PubMed:34048572, PubMed:36944332, PubMed:37257451, PubMed:37369679, PubMed:40793791). Demethylates RNA by oxidative demethylation, which requires molecular oxygen, alpha-ketoglutarate and iron (PubMed:21264265, PubMed:23177736, PubMed:24489119, PubMed:24616105, PubMed:24778178). Demethylation of m6A mRNA affects mRNA processing, translation and export (PubMed:23177736, PubMed:34048572, PubMed:36944332, PubMed:37257451). Can also demethylate N(6)-methyladenosine in single-stranded DNA (in vitro) (PubMed:24616105). Required for the late meiotic and haploid phases of spermatogenesis by mediating m6A demethylation in spermatocytes and round spermatids: m6A demethylation of target transcripts is required for correct splicing and the production of longer 3'-UTR mRNAs in male germ cells (By similarity). Involved in paraspeckle assembly, a nuclear membraneless organelle, by undergoing liquid-liquid phase separation (PubMed:37369679, PubMed:37474102). Paraspeckle assembly is coupled with m6A demethylation of RNAs, such as NEAT1 non-coding RNA (PubMed:37474102). Also acts as a negative regulator of T-cell development: inhibits gamma-delta T-cell proliferation via demethylation of JAG1 and NOTCH2 transcripts (By similarity). Inhibits regulatory T-cell (Treg) recruitment by mediating demethylation and destabilization of CCL28 mRNAs (By similarity). {ECO:0000250|UniProtKB:Q3TSG4, ECO:0000269|PubMed:21264265, ECO:0000269|PubMed:23177736, ECO:0000269|PubMed:24489119, ECO:0000269|PubMed:24616105, ECO:0000269|PubMed:24778178, ECO:0000269|PubMed:34048572, ECO:0000269|PubMed:36944332, ECO:0000269|PubMed:37257451, ECO:0000269|PubMed:37369679, ECO:0000269|PubMed:37474102, ECO:0000269|PubMed:40793791}. This is the function of Ensembl gene identifier ENSG00000091542 (ALKBH5, alkB homolog 5, RNA demethylase).