The requierements for a patent are
Novelty is anchored in 35 USC 102, which reads
(a) NOVELTY; PRIOR ART.—A person shall be entitled to a patent unless—
(1) the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention;
(2) the claimed invention was described in a patent issued under section 151 , or in an application for patent published or deemed published under section 122(b) , in which the patent or application, as the case may be, names another inventor and was effectively filed before the effective filing date of the claimed invention.
(Leaving out everything that follows because it treats special cases and isn't relevant here)
Assuming the reason you know about the patent in South Korea is because the South Korean patent application has been published 35 USC 102 (a) (1) contains your answer -> it will get denied if the prior art publication (the korean patent) is found by the examiner.
If it hasn't been published the situation is a little more complex. (For a complete answer see here), in summary, if the patent application is ever published, it can be held against your US application.
If you are named as an inventor on the korean application, the situation is even more complex, but I assume from your question that you are not, so I won't elaborate.