The 1890 Half Dollar has a small mintage of only 12,000 pieces, which is actually on the high-end of the Half Dollar dates from the late 1800's. Even so, it is fairly common in Mint State thanks to prescient collectors of the time, who set aside nice examples before they entered circulation. The 1890 Half Dollar is slightly less common that the 1888 and 1889. but nowhere near as common as the 1891. The most common Mint State grade is MS64, but other grades from MS62 to even MS66 are always available. In MS67, the 1890 Half Dollar is very rare.
As is typical of Half Dollars of this period, the surfaces on the 1890's are usually Prooflike and, as a result, they are often confused with Proofs. However, Proofs are slightly less valuable, so certification is recommended highly to get the attribution correct.