Open Port: 80
Open Port: 2468
Open Port: 5678
Open Port: 6688"
Well, port 80 is your webserver. Not sure about the other ones, though; chances are they're just temporary ports opened by applications. When you do a portscan, do you get the same three ports over and over again, or do the port numbers change?
"Search the internet, and found the port 5678 is reserved"
Reserved ports only really matter for ports 0-1023; above that it's pretty much a free-for-all.
I know there's a way to figure out which process opened which port under WinXP, so hopefully there's an equivalent mechanism under OS X. You might try looking into that if you're still paranoid