Bank stocks may be enjoying a recent rally, but don't expect the good times to last, investing expert Jason Benowitz told CNBC on Thursday.

While financials have been one of the worst sectors in the this year, bank stocks got a boost after the major financial institutions passed the latest round of Federal Reserve stress tests last week. The SPDR S&P Bank ETF (KBE) is up more than 7 percent in the last month of trading.

"We don't that this is sustainable. We think the yield curve will stay relatively flat ... and that will pressure bank earnings," the senior portfolio manager at Roosevelt Investments said in an interview with "Power Lunch."

The yield curve refers to the relationship between short-term and long-term interest rates. Bank profits increase when long-term rates rise, making the curve steeper.