pop-up message

When I turned on my computer I  received a pop-up message saying that ..'computer 224(+other numbers)......is attempting to access systemuiserver (not sure of spelling) on your....(not sure of the rest because the message went away after about 15 sec).

There was a button asking me to accept or not accept.

 

What am I supposed to do with this message?  How am I supposed to know what that long computer number means?

 

Thank you,