Possibly, what is probably the case is that you don't have
Anti-Aliasing turned on, or not turned up high enough. Anti-aliasing does reduce frame rates, so it will depend on what sort of graphics card you have as to whether its worth turning it on or not.
Usually anti-aliasing is managed through graphics card drivers, or some sort of Graphics Card Control Panel firmware. Its hard to say the best way for you to give this a shot without further information.

Alex