Is it safe to have unprotected sex during menstruation?

Depends. When you say safe are you referrring to getting pregnant? If so then it is very unlikely you will get pregnant while on your period. Often people mistake other vaginal bleeding episodes for their actual period. If you do not want to be pregnant you should be on birth control and using condoms. Stds can be passed at anytime if sex is unprotected.
Unprotected sex. There is no time during the cycle that one is protected from sexually transmitted diseases. A female could become pregnant at the end of her period if she had a long period and a short cycle. It is best to consistently use protection if pregnancy is not desired.

Related Questions

A girl had unprotected sex about 3 days after her menstruation. She used contraceptives just to be on the safe side, after about 5 days she started menstruating again, what do you think is wrong?

Impossible to know. Without full history and exam would just be speculating. Is this really menstrual flow or bleeding of another cause? Irregularities of menses are quite common and due to multiple causes, so nothing may be specifically "wrong". Suggest that if the problem continues you see a gynecologist and be evaluated. Read more...
Breakthrough bleed. The use of the emergency contraceptive probably caused the uterine lining to swell and then shed after the contraceptive was withdrawn causing bleeding. Read more...