Mercedes sits in fourth place in the Constructors Championship, having claimed two pole positions and two podiums from the opening four events.
"We know that the car went very well at the Circuit de Catalunya in pre-season testing so I am hopeful that we can have a strong weekend," said Rosberg.
"It will be an interesting weekend and once we see how everyone performs in Barcelona, it should give a good idea of how the rest of the season will look."
Team-mate Lewis Hamilton reckons Mercedes now know where they need to find improvements.
"I'm feeling very comfortable in the car now and we know the areas that we need to improve so a lot of effort is being put in to close that gap to the front-runners. Barcelona should be a good test as we know the circuit so well having completed most of the pre-season test programme there."