If it's a wireless mouse and you're only just experiencing this, it might need to be charged or have the battery changed, it's happened to me the first time the battery ran low for me.
If not, clean the bottom of your mouse so the laser has a clear shot at your mouse pad.
Changing the surface your mouse is on affects it too, if you're using something different to put it on.
Several gaming mouses have options in their driver software to adjust the sensitivity (dpi).
I personally use this one, even though it "only" has 2 extra buttons, it works very well and even has weights so you can adjust how heavy the mouse is.
What I like most about it though is that it saves the macro or hotkey combinations and dpi settings you adjust inside the driver software even if you connect it to a new system. Ever since I configured it I've never had to re-configure it even though I've re-installed my OS several times and even own a new computer now.
But in short, some gaming mouses provide extra settings for it.
Naga can be set up to 5600 DPI, and trust me, it's incredibily fast - read annoying. That new Sensei I think it goes up to double that.
I found it fine with 800 DPI, then set up a tiny higher in games.
Science flies you to the moon. Religion flies you into buildings.
To resist the influence of others, knowledge of oneself is most important.