The Belgian has scored 10 goals in 13 Serie A appearances this season to help Napoli climb to the top of the table, and he insists he is happy to stay at the Stadio San Paolo.
Mertens said he opted not to pursue a transfer to Barca because of the stiff competition for places at Camp Nou, but the subsequent departure of Neymar to Paris Saint-Germain left him pondering his decision.
"Every now and then you feel like doing something different," Mertens told Belgian newspaper Het Laatste Nieuws. "I don't always go on vacation in the same place, but at this moment, a transfer is not in my plans.
"There was interest from them [Barcelona] for a while, but I would've been the reserve to Leo Messi, Luis Suarez and Neymar, so after a great year at Napoli I didn't want to go back on the bench, even if it was Barcelona.
"I decided to sign a new contract here and then Neymar went to Paris Saint-Germain, so the transfer market exploded.
"At times I think: 'What would I be like now at Barcelona?' I like to think that, because if you look at who has been playing on the left there in recent months, I could've played there."
Mertens, reinvented as a striker by coach Maurizio Sarri, scored 28 Serie A goals last season as Napoli finished third and established themselves as an exponent of some of the most attractive football played anywhere in Europe.
"The last 12 months have been insane. It's important to be happy. I know it won't get much better than this," he added.
"I know I'm not a Lionel Messi or a Cristiano Ronaldo. I don't see myself as a world-class player. Napoli's game is perfect for me. I will always get goals here.
"I received an offer from China: I would've earned an incredible sum. But Napoli didn't want me to go, and I wanted to stay. So nothing came of it.
"But what if an offer like that were to come in again? That's why I wanted a release clause in my new contract. It's true €28m isn't much for a Chinese club, and it's a decent sum for Napoli too.
"I have become a bargain! Where do you find a player who scores 28 Serie A goals and costs €28m? Nowhere, right? I negotiated well."