Is rubber a conductor

No it is an extremely poor conductor, being thought of as a good insulator, but if electricity at a high enough voltage , and the rubber trying to protect the current from escaping is too thin, then the current can jump across the insulation gap. Fortunately the manufacturers of electric cables, switches, dynamos and other everyday products like electric kettles, light fittings, the wiring of a house or a car know very well how much insulation is needed in whatever they make.

Workers involved with electrics will wear rubber shod boots, or stand on rubber mats, wear rubber gloves or other insulating materials, and why their tools are specially made; such as a screwdriver with a plastic handle, or wire cutters with insulated handles.
If you mean a conductor of electricity then no its not