No, this is normal.
When a mobile cpu is not working very hard, it drops it's multiplier down ( not it's FSB ). Yours appears to tick over at half speed, this cuts down on power usage and also cools the cpu. When you start to put pressure on the computer, it will make the cpu run at full power.
I take it that it's a 64bit sempron. If so then they have two different clock speeds. One at 1600Mhz and 2000Mhz.