I think that pedrocr is from Portugal so in case you're learning Brazilian Portuguese you should consider that Brazilians usually use "estar + present participle" where the Portuguese use "estar a + infinitive" (for example "estou a falar" vs. "estou falando").
Brazilians thus have "estar sendo" which can be used in many cases where English has "is being", but as a non-native speaker I'm not sure what I can claim about its connotations or whether it's the same as "estar a ser". But my initial guess is that the Portuguese say "estou a ser" just as they say "estou a falar", while Brazilians say "estou sendo" just as they say "estou falando".
Spanish-speakers in turn have "estar siendo" with the Spanish present participle of ser, like "estoy siendo". I suspect this is the standard form of this construction in all kinds of Spanish.