Terms of the company’s new lease with Irvine Co. were not disclosed. Other space at MacArthur Court counts monthly rents running from $1.90 to $2.70 per square foot, according to the Newport Beach-based landlord’s website.

News of Clean Energy’s upcoming relocation comes a little more than a month after its current offices in Seal Beach were sold to San Diego-based Parallel Capital Partners Inc. in an $85 million deal. It is the largest office sale seen in OC so far this year.

Reinvestment, Redesigns

Clean Energy stands to become the largest tenant at MacArthur Court, which has seen some notable additions and expansions in the past few months, following what officials at Irvine Co. called a “significant reinvestment” in the property last year.

Other companies moving to the complex include Santa Ana-based MSC Software Corp., which also will relocate its headquarters to 4675 MacArthur later this year after inking a nearly 36,000-square-foot lease.

William Lyon Homes, which last week filed paperwork for a $200 million initial public offering, moved its headquarters to MacArthur Court earlier this year.

“After a significant reinvestment in 2012, MacArthur Court is seeing strong interest from a broad spectrum of customers,” Steve Case, executive vice president of Irvine Co.’s office division, said in a statement.

Improvements to the property include a new on-site gym, remodeled conference centers and an open-air plaza, according to Case.

Some of the more notable upgrades to the property of late are tenant-driven.

The Newport Beach office of San Francisco-based architecture firm Gensler, which already had its local office 4675 MacArthur, is expanding into about 23,000 square feet of space on the first two floors of the building.

Gensler is now putting the finishing touches on a redesigned ground floor at the office, which the firm describes as having elements of a “modern beach house” along with a number of environmentally friendly features.