LAN IP behind NAT is registering on Asterisk


I am using EyeBeam on the client side and a hosted Asterisk on the server side located at a Data Center in USA.

When I hit this command --> /usr/sbin/asterisk -rx "sip show channels"
I see this output:

Peer             User/ANR    Call ID      Seq (Tx/Rx)  Format           Hold     Last Message    (None)      YzMyZWM0ZWF  00101/00208  0x0 (nothing)    No       Rx: REGISTER    (None)      MmY2ZmE4MmN  00101/00004  0x0 (nothing)    No       Rx: REGISTER    (None)      YjcyNDIxMWR  00101/00014  0x0 (nothing)    No       Rx: REGISTER     1760362286  e69264d3605  00101/00102  0x100 (g729)     No       Rx: ACK  1003        4e52d59053f  00102/00000  0x100 (g729)     No       Tx: ACK     1217333333  fb47a9391ad  00101/00102  0x100 (g729)     No       Rx: ACK

Why and how are is the LAN IP (192.168.1.xx) registering on the trixbox. All my PCs are behind a DSL router and the packets are getting natted.

The 192.168.x.x records will disappear after some time automatically and reappear after some time.

I am unable to understand this …
This is normal or a problem situation ??

Please advice.