Condensation in your attic can cause damage over a period of time, and should be addressed. It is caused by heated air escaping into the attic and condensing on the cold attic surfaces. The first step to solve the problem is to identify air leaks from house. these can be from light fixtures, ceiling exhaust fans, or a poor sealed ceiling. When looking at light fixtures, you want to see a nice tight fit from the sheet rock, and wire passages should be sealed. When looking at your exhaust fans, they should fit to the ceiling tight also. However you will need to get in your attic to be sure the vent pipe is connected to the fan and protrudes above the roof sheeting, with a roof vent covering it. While you are in the attic be sure to check the attic ventilation as well. When you look at the bottom edge you should see some vents or holes, and most likely daylight. The upper side of your roof should also have a vent system, which would be can vents or ridge vent. When you look at these vents you should also see some daylight. Here are a few photos of bad attic condensation.
If you have done all of the checks and are still getting some condensation, which is possible, there are some other remedies. First would be to use the exhaust fans in your bathroom and kitchen for longer periods of time when showering and cooking. Second would be to run a dehumidifier in the house. In most cases this would only need to be done when the weather is really cold.
Here is a link from Cornell University with much more info about attic condensation. http://www.human.cornell.edu/dea/outreach/upload/attic-condensation-2.pdf