Rosberg missed out on the title in the last race of the season, when team-mate Lewis Hamilton won the final race of the season in Abu Dhabi. The pair became fierce rivals over the course of the 2014 season as they competed for the world championship.
The German driver revealed that he did not spend long dwelling on his disappointment and that he is already looking ahead to next season.
He said: "Thankfully it goes pretty quickly, when there is success or not success, it takes a few days and I get over it.
"In this case that was great, when it is successful it is not so great as you want to enjoy the moment longer, but it is quite short lived always.
"I am ready to go again definitely, it's been a long break."
Rosberg added: "The biggest challenge first of all is to be my best – that is the first and most important challenge for me – and to be better than ever.
"Then the second challenge is going to be first of all trying to beat Lewis and then further more trying to beat all the other teams – we have no idea where we stand so we need to wait and see where we are. Of course we had very strong base last year so the chances are good, but we don't know."