My daughter is 5 Years old. When ever a family member comes to visit she cling to them and don't let go. What causes her to behave this way? She gets a lot of attention from my husband and me.

It could be that since she is used to getting a lot of attention form you,

She expects it and enjoys it from everybody.

Is there any other behavior that causes you concern? Because children are individuals.
Some are clingy, some are shy and quiet , some are loud and obnoxious and all are fairly normal kids.

If this is the only behavior of hers that you are concerned with , I don't think it is a problem.
I do realize that I am basing this on a very limited amount of information.
But as you have described it , it seems to be a 5 yr old who likes attention .
Nothing too unusual about that.

You said that she is clingy with family members when they visit. So, these people are familiar to her, and she is comfortable with them.

When you say clingy, what do you mean. Does she talk a lot to the person, want to play with them, show them her toys/artwork, bring them toys, etc.

Or, is she sullen, withdrawn, just sits very near to the person and doesn't say, or do a thing.

And, is she like this with strangers who visit, or people other than family members.

I knew a little girl like this. She was a girlfriend's niece, named "Jennie". Even though there were children all around, she latched onto me, every visit. She was the sweetest little girl I've ever seen. I have no ideas what causes this, but I can tell you that she turned out to be one of the best parents, and person, that I've come across. She's "normal", and very loving.

I wouldn't be worried at all.