Not much in the way of confirmation on this yet, but from WBAL, the NBC affiliate in Baltimore:

Developing: FBI confirms agents are executing a search warrant at the office of GOP Fundraiser/Consulting firm in Annapolis

Update:

FBI investigation of GOP fundraising firm in Annapolis is run out of Washington, not a local case

Annapolis firm targeted by FBI touted for pioneering the use of technology in political campaigns. Represents GOP candidates nationwide

Update #2:

A report from the Capital Gazette says the action is in the vicinity of Main St., which BTW is the street that Strategic Campaign Group as well as Red Maverick Media are on.

Agents from the Federal Bureau of Investigations were in Annapolis Thursday to investigate an organization with offices in the vicinity of Main Street, a spokesperson for the bureau confirmed.

Media reports on Twitter linked the site of the activity to the address of a Republican fundraising and consulting firm. FBI officials wouldn't confirm whether their investigation was linked to the organization.

FBI spokeswoman Lindsay Ram said the investigation is being conducted through the bureau's Washington field office, which has jurisdiction in Washington, D.C. and Northern Virginia. She said agents from the office sometimes cross over into other jurisdictions when the entity they are investigating has offices in multiple locations.

This is developing story, and will be updated as more details become available.