Yes a fan is good for the plant as it makes the plant grow stronger. Plants need fresh air though, what I do is hang a extractor fan out the window for 2hrs a day, this brings fresh air in from outside in to my growroom, i've only done this for a few days & plants have started growing nicely.
Dude0
PS... extractor fans are extremely cheap, I got one for £6 & ducting for £5.