Production-wise: Maybe (since we're still in season 3)
Airing-wise: More likely than above.
Miranda said that they would begin filming the next season early 2011, but that could either mean they split up the third season in half (like they did for season 2), and that they would film the rest of the season because 26 episodes were ordered; or, it is an entire new season.
If it IS a new season, it's season 4 in production order. But if we're talking about in airing order, then it will be season 5 (but only if they go on with filming the next season).