My iPod Touch has blocked

Hi!

Yesterday evening I listened some music on my iPod Touch and, in the same time,
I was surfing on the 'net. At a certain point, after I gave a command to open a new web page, my iPod Touch has blocked. It looked like it would be "frozen" - no commend worked. I clicked the ON/OFF button and my iPod Touch restarted only after 3-5 minutes.

It is normal to have such "frozing" or... I should worry?...

Thanks!