WDrR3600 is not a switch but a router. Does it make a difference?
What kinds of activity did you refer to? How did you "observe" it?

Dear Ada,
Thank you for your response.
I do not plug WAN port of the TL-WDR3600. I have another router with 4-ports, One is connected to output of one lan port of the TL-WDR3600. Another port is linked with another switch.
I see activity with led activity. When all computers are off it still remains activity led of all connections between swicth and they are all blinking. If I remplace the TL-WDR3600 by my old switch, activity leds do not blink.

Hi Plomox

WDR3600 is a router, a functional and advanced router in fact.
It has a lot of active behaviors such as IGMP query, arp query, etc even there is no other hosts talking with it.
Nothing has to be worried. It just cannot be totally behave as same as a switch. A switch is passively forwarding frames.

If you do like to reduce the WDR3600's activities, you can disable DHCP, IGMP and IPV6 service on the WDR3600

Thank you !