What's more, ISSG said, it was the best month for corporate plans' funded status since January of 2011. 

Public plans, endowments and foundations also benefited, seeing their best month since February of last year, according to the BNY Mellon Institutional Scorecard. 

While Wilshire wasn't quite as optimistic about the amount of the increase – pegging it at 3.9 percent and boosting the funded level to 77.2 percent – it agreed that an increase in equities coupled with an even greater drop in liabilities accounted for the trend. 

How far pension funding ratios rise or fall is important because they indicate how much money funds have to set aside every year to ensure future retirees are paid. Funding ratios dropped to as low as 64 percent five years ago amid the financial meltdown, but the current funding levels still trail the 95 percent peak seen just before the Great Recession. 

Wilshire said that asset value increased by 1.7 percent on positive equity returns, and liability value fell by 3.5 percent, thanks to rising corporate bond yields. 

ISSG put the gain in asset value at 2.1 percent on gains in U.S. stocks, international developed markets equities and emerging markets equities. Liabilities dropped by 3.9 percent because of the Aa corporate discount rate rising 28 basis points to 3.84 percent.

"The funded status for U.S. corporate plans is now in positive territory for 2015," Andrew D. Wozniak, head of fiduciary solutions, ISSG, said in a statement. "February capped the best three-month period for job growth in the U.S. in the last 17 years, and the strengthening employment situation was one of the important drivers of interest rates in February."