Receive TCP RST packet from unreachable computer

Today I had a opportunity to work with wireshark.

I installed wireshark on my VMware and made some test on it.

And I found a interesting thing.

I sent the HTTP request to not exist computer and captured the all packet flow with wireshark.

The first packet was SYN packet.

And second one was re-transmission packet.(for system hadn't received any response from target computer).

But surprisingly, RST packet from the target computer reached.

I couldn't understand where this packet came from.

I tested for 2 target computers, and in both case, I had the RST packet.

So are there anyone answer about those suspicious RST packets?

Thanks for reading.

Regards.