2001 Honda Accord Electrical problem

When I drive, the electrical system seems lost power occasionally. Sometime it happens every minute, sometimes every 10-20minutes. Just happen randomly. When the problem comes, the audio system is off, maintain required light is on, power to the cigar lighter lost and the speedometer goes to very low (about 20 mph). It takes about a few seconds and then everything recovers to normal. I did not feel any abnormal for engine though. What could be the problem? Thanks