My Mom was issued a US tourist visa 3 years ago and it's valid for (5 years)... 2 years validity left now.. She didn't travel back then when she was granted a visa. She'll be coming to US now.. will there be a problem ? Can she travel anytime during the validity of the visa ? Can she be asked question about why she didn't come to US when the visa was granted 3 years ago ?

Any information would be appreciated

Thanks.

There will be no problem.My parents recently came here 4 yrs after getting the visa.No question asked.But if they ask just tell them to say anything like busy with some stuffs etc.
Just to give you peace of mind I have seen lot of people coming few yrs after getting visa. It's normal.

My parents were granted in Dec 08, but they didn't visit until may 11. Should be no problem.

Same here.. my parents came 3 years after getting the visa... no problem at all.

Most likely there will not be any problem at the port of entry, however, be prepared to answer questions like below if the immigration officer inquires - just in case:

Why did you not come when you got the Visa 3 years ago?
Why are you visiting now? | What is the purpose of your visit?

Again, most likely their entry to the US will be hassle free, but just in case they are asked questions like these, they will be prepared to answer. Good Luck to them!

It doesn't matter until and unless visa is valid but make sure passport is valid too