The Emnid Sunday poll for Bild newspaper showed support for Merkel's bloc unchanged at 38 percent, while the SPD support dropped 1 percentage point to 25 percent.
The SPD got a boost after nominating Martin Schulz in January as Merkel's rival for chancellor in September's election, but has slipped recently after several state election losses, AP reported.
The pro-business Free Democrats and Greens both gained a point to 8 percent support, putting them at the same level as the Left Party, which dropped a point, and the nationalist Alternative for Germany party, which was unchanged.
The poll's margin of error was plus or minus 2.5 percentage points.