When someone new comes to one of your meetings, it is very important that they are made to feel welcome. Go over to them, greet them, maybe give them a hearty 'Saluton!' You'll need to inquire as to their proficiency before launching into full blown Esperanto.
Introduce them to the other members, and maybe pair them up with a 'buddy' for the meeting. Connections to others are important to newcomers, otherwise they may assume it's a closed group and never return.
You definitely do not want to ignore them or go on with your conversation other than to excuse yourself for a moment. Having entered the room to several (non Esperanto) groups, I cannot stress the need to be recognized and welcomed as soon as possible.