Athlons run very cool, that small overclock shouldn't make it overheat.
But we do need to know what board you are running? And does it have Vcore control? If you leave it on auto voltage, it usually runs more than necessary which makes extra heat.
As someone else mentioned, overclocked via the bus speed overclocks the ram and hyper transport clocks. So, we also need to know what ram you are running as well.