In ABO blood grouping, Do a person with A blood group have anti-B antibodies already?

Yes.

A type A person (with no B antigens on their RBCs) develops anti-B during the first few months after birth. Apparently dust mites, mold spores, etc., have antigens that are very much like the A and B antigens on our RBCs. All of us are constantly exposed to such environmental factors, and in response, our immune system makes anti-A or anti-B, or both, or neither, depending on whether the A antigen or the B antigen (or both or neither) is foreign to us.

So the plasma of a type A person contains anti-B, a type B person has anti-A, a type AB person has neither antibody, but a type O person has both anti-A and anti-B.

An excellent review of red cell antigens/antibodies may be found at the National Library of Medicine web page, listed below:

http://www.ncbi.nlm.nih.gov/books/NBK2261/

Also, to complete an earlier answer, type O plasma contains naturally occurring anti-A, anti-B AND anti-AB antibodies. Anti-AB antibodies are a unique antibody directed against a separate antigenic site from the A or B antigens, and is only produced by type O individuals.

NO, A blood group individuals normally do not possess Anti-B Antibodies in their blood plasma. Only if B group blood is transfused into their veins, the plasma produces Antibodies.

No, A blood group have antigen A&antiabody b. If A blood group person transfus to B blood group person the blood is clump or aggulitenet. A blood group only give for A&AB blood person.