My gas heater comes to temperature but when it turns off after reaching the temperature it comes on and goes off about 5 to 6 times for a few seconds. It will come on for a second and then shut off, then come on for 5 seconds and shut off then on again and off again about 3 more times. I think it is just the fan because it wouldn't have time to light the gas and it wouldn't need to since it came up to the set temperature. Then it stops and stays off till it needs to come on again and when it reaches the temperature again and it does the whole thing again when it turns off after reaching the set temperature. What is going on? This is a new development which started happening a couple of days ago. It is not exceedingly cold, in the 50's and 60's.

Make and model of furnace? What type of thermostat? Sounds like the unit is short cycling. Could be caused by a number of things. Dirty flame senser, malfunctioning thermostat, bad control board, high limit, aux limit, just to name a few.