This was rather inevitable, given the success and the fans. The Flash has gathered - this isn't official yet, since CW didn't confirm this yet. However, more and more scoops have appeared and each of them say that a second season will follow.
The numbers says it all - in the 18-49 demo, The Flash has an average of 1.53, which means about 4 million viewers per week. In comparison, Arrow (which is in its third season) averages a score of just 1.01 with just (if it can be said so) 2.79 million viewers.
Source: Comic Book Movie