Definitely not...CBR500 series is a solid bike...but they make very little hp for their displacement, and also weigh a ton, both so they fit into the A2 classification. A Ninja 300R is probably a lot faster both in the straights and in the corners.
I don't know the original sources but, according to http://www.zeroto60times.com/:
R3 = 0-60 in 5.1 & 1/4 mile in 14.1
Ninja 300 = 0-60 in 5.6 & 1/4 mile in 14.6
And then found this from another forum:
CBR500R: Corrected 1⁄4-mile: 13.63 sec. @ 93.80 mph
Ninja 300: Corrected 1⁄4-mile: 14.23 sec. @ 89.85 mph
So the CBR is more than half a second faster in the quarter mile than a Ninja 300. I think my point still stands that the R3 is faster than the Ninja but the CBR500 still edges out the R3 slightly.