Nevertheless, that does not mean munis are exempt from any declines. The current weakness is expected to extend for a while if the Federal Reserve continues to push up interest rates, and market supply and demand factors become more negative.

The municipal bond market has also benefited from a diminished supply in debt issues as a result of the tax reform bill passed last year. Due to the uncertainty over the tax-exempt status of muni incomes, along with other potential rule changes in the market, issuers originally inundated the market with new issuance at the end of the last year, which lead to one of the worst January months for munis on record but cleared out any new supply that would have hit the market for 2018.

“The low supply of bonds has definitely helped the market this year,” Brian Nick, chief investment strategist at Nuveen, told CNBC.

For more information on the munis market, visit our municipal bonds category.