Is the word atrás the same in Brazilian and European Portuguese?

No

While the spelling and core meaning of "atrás" are identical in both Brazilian and Continental Portuguese, there are differences in typical usage and pronunciation.

• Usage (Time): In Brazil, it is very common and natural to use "atrás" redundantly with the verb há (e.g., "há dois anos atrás"). In Portugal, this is considered a pleonasm (redundancy) and is generally avoided; a Portuguese person would simply say "há dois anos."
• Usage (Position): In Brazil, "atrás de" is the standard way to say "behind." While "atrás de" is understood in Portugal, Portuguese speakers much more frequently use the alternative phrase "por trás de" to describe physical position.
• Pronunciation: Brazilian Portuguese features more open, clearly articulated vowels. In Continental Portuguese, unstressed vowels are heavily reduced; for instance, the initial "a" in "atrás" is often almost silent, making the word sound more like "traz."

Brazilian Portuguese Examples

1. "O cachorro está atrás do sofá." (The dog is behind the sofa.)
2. "Eu estudei isso dois meses atrás." (I studied this two months ago.)
3. "Não olhe para trás agora." (Don't look back now.)
4. "Ele mora atrás daquela padaria." (He lives behind that bakery.)
5. "A mala ficou atrás da cadeira." (The suitcase was left behind the chair.)

Continental Portuguese Examples

1. "O cão está por trás do sofá." (The dog is behind the sofa.)
2. "Eu estudei isso há dois meses." (I studied this two months ago.)
3. "Não olhes para trás agora." (Don't look back now.)
4. "Ele mora por trás daquela padaria." (He lives behind that bakery.)
5. "A mala ficou por trás da cadeira." (The suitcase was left behind the chair.)