The former Blaugrana defender was offered the job as Ernesto Valverde's successor but turned it down to stay with the Netherlands ahead of Euro 2020.
"I received a call from Barcelona," Koeman told Catalunya Radio.
"I have to keep to my word with the Dutch national team and play at the European Championship.
"At the moment, the national team is more important. No one knows what could happen in the future.
"In my contract, I have the possibility to leave the national team after the European Championship, but it's not the time to think about that because I'm really happy with my job with the Netherlands.
"Everyone knows it's my dream to coach Barcelona one day and let's hope I have another chance in the future.
"It always depends on your journey. I know that, as a coach, you have to have lots of experience to coach a team like that."