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

No. While the spelling and core meaning of the word are identical, there is a significant difference in typical usage and grammatical construction. In Brazilian Portuguese, the gerund form (mentindo) is the standard way to express an ongoing action. In Continental Portuguese, this construction is much less common; instead, the preposition a + infinitive (a mentir) is the natural and standard way to express the same idea.

Brazilian Portuguese Usage

1. Você está mentindo para mim. (You are lying to me.)
2. Ele está mentindo sobre o trabalho. (He is lying about work.)
3. Eu não estou mentindo, eu juro! (I am not lying, I swear!)
4. Ela foi pega mentindo para o marido. (She was caught lying to her husband.)
5. Por que você está mentindo para a gente? (Why are you lying to us?)

Continental Portuguese Usage

1. Tu estás a mentir-me. (You are lying to me.)
2. Ele está a mentir sobre o trabalho. (He is lying about work.)
3. Eu não estou a mentir, a sério! (I am not lying, seriously!)
4. Ela foi apanhada a mentir ao marido. (She was caught lying to her husband.)
5. Porque é que estás a mentir-nos? (Why are you lying to us?)